Minnesota Taconite Workers Health Study: Environmental Study of Airborne Particulate Matter in Mesabi Iron Range Communities and Taconite Processing Plants — Mesabi Iron Range Community Particulate Matter Collection and Gravimetric Analysis Submitted by: Stephen D. Monson Geerts1, George Hudak 1, Virgil Marple2, Dale Lundgren3, Lawrence Zanko1, and Bernard Olson2 1Natural Resources Research Institute, University of Minnesota Duluth 2Department of Mechanical Engineering, University of Minnesota Twin Cities 3University of Florida - Gainesville
Date: December 2019 Report Number: NRRI/RI-2019/30 – December– 2019 Project No. 1806-10416-20080
NRRI Report of Investigation Investigation of Report NRRI
Duluth Laboratories & Administration 5013 Miller Trunk Highway Duluth, Minnesota 55811
Coleraine Laboratories One Gayley Avenue P.O. Box 188 Coleraine, Minnesota 55722 Visit our website for access to this and other Natural Resources Research Institute publications: http://www.nrri.umn.edu/publications.
Cover Photo Caption: Mesabi Iron Range community ‘rooftop’ particulate matter sample and data collection setup – Keewatin Elementary School – Keewatin, Minnesota.
Recommended Citation: Monson Geerts, S.D., Hudak, G., Marple, V., Lundgren, D., Zanko, L., and Olson, B. 2019. Minnesota Taconite Workers Health Study: Environmental Study of Airborne Particulate Matter in Mesabi Iron Range Communities and Taconite Processing Plants: Mesabi Iron Range Community Particulate Matter Collection and Gravimetric Analysis. Natural Resources Research Institute, University of Minnesota Duluth, Report of Investigations NRRI/RI-2019/30. 151 p.
Key words: taconite, Mesabi, particulate matter, airborne, community, sampling, gravimetric, amphibole, cleavage fragment, elongate mineral particle EMP
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UNIVERSITY OF MINNESOTA DULUTH – NATURAL RESOURCES RESEARCH INSTITUTE
ENVIRONMENTAL PARTICULATE MATTER CHARACTERIZATION Taconite workers on the Mesabi Iron Range (MIR) in northeastern Minnesota have displayed a higher than normal incidence of the rare disease Mesothelioma (MDH, 2007). To better-understand this higher level of occurrence, the Minnesota Legislature funded the $4.9-million-dollar Minnesota Taconite Workers Health Study (MTWHS). Initiated in 2008, this five-component study was a collaborative effort between the University of Minnesota’s School of Public Health (SPH), the University of Minnesota Medical School (UMMS), and the University of Minnesota Duluth’s Natural Resources Research Institute (NRRI). The University’s School of Public Health and Medical School performed the study’s four health- related components (Finnegan and Mandel, 2014). The study’s fifth component, “Environmental Study of Airborne Particulate Matter,” was conducted by the NRRI and is summarized in this Executive Summary Report. The study comprised physical, mineralogical, and chemical characterization of airborne particulate matter (PM) in MIR taconite processing facilities and selected MIR communities. Respirable mineral PM of a specific size, shape, and mineralogy – referred to as elongate mineral particles (EMPs) – were of special interest. Ambient aerosol PM samples were collected from five MIR communities, three Minnesota background locations, and the six operating taconite processing plants located on the MIR. Components of this PM characterization included: gravimetric analysis, mineralogical identification, mineralogical concentration evaluations, PM morphological characterizations, and PM chemical characterizations. The fundamental question addressed by this study is, “What is in the air?” Additionally, a characterization of EMPs from age-dated lake sediments in two MIR lakes was performed in an effort to obtain historical data regarding the characteristics of past PM conditions; in a general sense, to investigate what had been in the air. Consequently, the research effort focused on providing answers to the following underlying questions: . How much PM is in the air? . What is the size distribution of the PM in the air? . What are the physical characteristics of the PM in the air? . What are the mineralogical characteristics of the PM in the air? . What are the chemical characteristics of the PM in the air? and . What historical trends in PM mineralogy, physical characteristics, and chemical composition can be identified from studies of dated sedimentary deposits in lakes located in close proximity to taconite operations on the MIR?
Disclosure and Disclaimer Statement The NRRI’s aerosol PM sampling protocols—including the equipment utilized and the data collected in this study—are not meant to represent, or to be considered a substitute for, ambient air monitoring as conducted and reported by regulatory agencies such as the Minnesota Pollution Control Agency (MPCA), Minnesota Department of Health (MDH), and the United States Environmental Protection Agency (USEPA). Any reference to State, USEPA, National Ambient Air Quality Standards (NAAQS), Occupational Health and Safety Administration (OSHA), and/or Mine Safety Health Administration (MSHA) standards is for illustrative and comparative purposes and is meant only to provide context to the findings in this NRRI study.
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EXECUTIVE SUMMARY: COMMUNITY GRAVIMETRIC STUDY As part of the NRRI’s “Environmental Study of Airborne PM on the Mesabi Range of northeastern Minnesota,” the NRRI conducted a “Mesabi Iron Range (MIR) Community Particulate Matter Collection and Gravimetric Analysis.” This study encompasses results from a total of 54 separate aerosol PM sampling events that were conducted at five MIR communities in northeastern Minnesota as well as three background sites. From west to east, the MIR communities sampled included Keewatin, Hibbing, Virginia, Babbitt, and Silver Bay. These communities were chosen for their spatial distribution across the 110-mile-long MIR, their relevance as population centers, their proximity to the six taconite processing plants, and the geological attributes of the Biwabik Iron Formation (BIF), the source of the taconite ores mined in northeastern Minnesota. In conjunction with the sampling at MIR communities, 24 aerosol PM samples were also collected from three background sites, including: Ely (rural and north of the MIR), Duluth (mid-sized city and south of the MIR), and Minneapolis (large metropolitan/industrial area not in northeastern Minnesota). The rural Ely Fernberg site is well recognized and maintained as an aerosol sampling site because of its isolated/“undisturbed” location in northeastern Minnesota. It is the background location of many regulatory agencies and research institutions. All five MIR communities and background sites were sampled at least three times during both summer season (defined as May through October) and winter season (defined as November through April). Community and background sampling events consisted of 120- to 168-hour sample collection events, with air sampling occurring at a rate of approximately 30L/minute. Equipment utilized in sample collection included a Micro-Orifice Uniform Deposit Impactor (MOUDI: Marple et al., 1991; 2014), a device that collects a size-fractionated sample of PM with aerodynamic diameters ranging from 30.0 to 0.056 micrometers (µm or microns), and a Total Filter Sampler (TFS), which collects non-size fractionated PM on a single substrate. The NRRI’s aerosol PM sampling and characterization is not meant to represent, or to be considered a substitute for, ambient air sampling as conducted and reported by regulatory agencies in the state of Minnesota; neither is it intended to be used for purposes of calculating exposure or risk assessment. References in this report to Minnesota ambient air quality standards (MAAQS), USEPA national ambient air quality standards (NAAQS), OSHA, and MSHA standards are for illustrative and comparative purposes only and are meant to provide context to the findings in this study. The findings from this report, which focuses on gravimetric analysis of aerosol PM collected from the MIR communities and background sampling sites, are as follows: 1. All MIR community samples have PM concentrations below PM concentrations set forth as NAAQS limits for PM10 and PM2.5. Please see the “Disclosure and Disclaimer” statement on page ii. 2. A comparative statistical analysis of PM10 and PM2.5 concentration variances was performed for community sampling conducted by the NRRI during this project and for regulatory sampling conducted by the MPCA over 10+ years at the same community sampling sites. Taking into account the increased sample collection times used by the NRRI (120–168 hours), the comparison showed that the overall statistical power of the NRRI sampling was in good agreement with the MPCA, producing confidence rates ranging from 85% to 95%. 3. The equipment and methods of sample collection used by the NRRI to characterize PM in the five MIR communities, including the three Model 120 MOUDI II cascade impactors, were in good agreement and shown to provide consistent measurements throughout the sample collection period (Marple et al., 2014). Statistical analysis indicates that PM2.5 and PM10 collected by NRRI from the Virginia site (2009) using MOUDI samplers showed no significant difference with PM2.5 and PM10 concentrations utilizing high-volume samplers associated with state regulatory sampling (MPCA, 2010) that was performed using USEPA-approved protocols. A detailed explanation of all statistical analyses can be found in the Sample Methodology – Preliminary Statistical Analysis section of this study report.
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4. An index called the “Taconite Particle Source Index” (TPSI) was assigned to each sample with the intention of correlating PM concentrations (PM1, PM2.5, PM10, Coarse= ≥ PM2.5 ≤ PM10, MOUDI total) with meteorological data collected at the time of sampling. The index largely represents the percent time that winds greater than 1.8 meters/second (~4 mph) were blowing from a potential source of mining-related particulate matter (including: mine pits, haul roads, tailings basins, and active waste rock piles) and local taconite processing facilities/plants. Significant correlation between PM and TPSI was found in the communities of Virginia (negative) and Babbitt (positive). Significant correlation between PM and TPSI were not found in the other three community locations that were sampled for this study. 5. Statistical analysis concluded that there was no significant difference in mean PM concentration levels (PM1, PM2.5, PM10, Coarse= ≥ PM2.5 ≤ PM10, MOUDI total) at the five MIR community locations when local mine/plants were active (operating) compared to when they were inactive (temporary shutdown periods). Similarly, there was no significant difference identified for these PM concentrations between MIR communities and the Ely background location. 6. Average winter season PM concentrations (PM1, PM2.5, PM10, Coarse= ≥ PM2.5 ≤ PM10, MOUDI total) were significantly higher than summer season PM concentrations. 7. Specific MOUDI total PM average concentrations (measured in µg/m3) from samples collected (n=number of samples) using the MOUDI Cascade Impactor in the five MIR community locations are as follows (Table A):
Table A. Average MOUDI Total PM concentrations (in µg/m3)for all sampling events, sampling events during plant inactivity, and sampling events while plants were active for Mesabi Range communities and background sampling sites away from the Mesabi Range. MOUDI Total PM Average Inactive Plant Active Plant Keewatin Elementary School 9.07 9.49 (n=6) 6.55 (n=1) n=7 (2.91)* (2.95) (NA) Hibbing High School 10.61 10.76 (n=3) 10.54 (n=6) n=9 (3.05) (4.24) (2.77) Virginia City Hall 12.70 13.11 (n=4) 12.43 (n=6) n=10 (3.75) (3.46) (4.24) Babbitt Municipal Building 10.41 9.59 (n=7) 11.04 (n=9) n=16 (3.38) (2.29) (4.06) Silver Bay High School 11.42 9.94 (n=7) 13.49 (n=5) n=12 (4.82) (3.70) (5.84) BACKGROUND Ely Fernberg Site 8.15 Not Applicable Not Applicable n=6 (3.63) Duluth NRRI Building 8.43 Not Applicable Not Applicable n=12 (4.35) Minneapolis UMN Mech. Eng. 15.25 Not Applicable Not Applicable n=6 (3.08) *(standard deviation based on concentrations)
Since there are no ambient air standards for “total PM,” PM10 is used for comparative purposes. Note that the PM2.5 and PM10 standards have evolved over time. The USEPA 3 revoked the annual PM10 NAAQS in 2006 (which had been 50 µg/m ), so only the 24-hour
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standard of 150 µg/m3 currently applies and is not to be exceeded more than once per year on average over a three-year period (USEPA, 2013). 3 8. The PM2.5 concentrations (measured in µg/m – and by representative percent of total sample) obtained from MOUDI sampling in the five MIR community locations are as follows (Table B):
3 Table B. PM2.5 concentrations (in µg/m )for all sampling events, sampling events during plant inactivity, and sampling events while plants were active for Mesabi Range communities and background sampling sites away from the Mesabi Range. PM2.5 represents the concentration of all particulate matter having an aerodynamic diameter less than or equal to 2.5 µm (Hinds, 1999, p. 255; https://www.epa.gov/air- trends/particulate-matter-pm25-trend).
PM2.5 Fraction of MOUDI Total Average Inactive Plant Active Plant Keewatin 6.54 (72.5%) 6.92 (73.7%) 4.27 (65.1%) n=7 (2.08)* (2.00) (NA) Hibbing 6.45 (61.2%) 6.75 (63.6%) 6.31 (60.0%) n=9 (1.92) (2.38) (1.88) Virginia 7.04 (55.7%) 7.69 (57.8%) 6.61 (54.4%) n=10 (2.23) (2.62) (2.08) Babbitt 6.64 (62.8%) 5.63 (57.5%) 7.42 (67.0%) n=16 (2.64) (2.08) (2.86) Silver Bay 6.37 (56.5%) 5.78 (58.5%) 7.18 (53.6%) n=12 (2.75) (2.39) (3.28) BACKGROUND Ely Fernberg Site 5.83 (71.5%) Not Applicable Not Applicable n=6 (2.73) Duluth NRRI Building 5.21 (66.9%) Not Applicable Not Applicable n=12 (1.94) Minneapolis UMN Mech. Eng. 9.73 (63.5%) Not Applicable Not Applicable n=6 (2.24) *(standard deviation based on concentrations)
3 For comparative purposes, the NAAQS PM2.5 limit value is 12 µg/m – three-year average of the annual arithmetic mean for a given monitor must not exceed; or 35 µg/m3 – three year average of the 98th percentile of 24 hour concentrations must not exceed (USEPA, 2013). 9. The Minneapolis background site had the highest average MOUDI total PM (15.25 µg/m3) 3 and PM2.5 (9.73 µg/m ) concentrations of the study, while Virginia had the highest average 3 3 MOUDI total PM (12.70 µg/m ) and PM2.5 (7.04 µg/m ) concentrations of MIR communities (see Tables A and B above). Ely had the lowest average MOUDI total PM (8.15 µg/m3) and 3 Duluth the lowest PM2.5 (5.21 µg/m ) concentrations of the study, while Keewatin had the 3 3 lowest average MOUDI total PM (9.07 µg/m ) and Silver Bay the lowest PM2.5 (6.37 µg/m ) concentrations of MIR communities. Those relationships can be viewed graphically in Figure 17 in the body of this study report.
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TABLE OF CONTENTS
ENVIRONMENTAL PARTICULATE MATTER CHARACTERIZATION ...... i Disclosure and Disclaimer Statement ...... i EXECUTIVE SUMMARY: COMMUNITY GRAVIMETRIC STUDY ...... ii LIST OF TABLES ...... vii LIST OF FIGURES ...... ix LIST OF PHOTOS ...... xi INTRODUCTION ...... 1 BACKGROUND ...... 1 What is Mesothelioma? ...... 2 REGULATION CONCERNING PARTICULATE MATTER (PM) ...... 3 OBJECTIVES ...... 9 Questions to be addressed ...... 9 SAMPLING METHODOLOGY ...... 10 Preliminary Statistical Analysis ...... 12 STUDY AREA ...... 15 Regional Geology ...... 17 Taconite Mines and Processing Plants ...... 18 Background (Community) Sampling Sites ...... 18 Ely Fernberg Site ...... 19 Duluth – Natural Resources Research Institute (NRRI) ...... 19 Minneapolis – University of Minnesota Mechanical Engineering Building ...... 19 MIR Community Sampling Sites ...... 19 Keewatin Elementary School...... 20 Hibbing High School ...... 20 Virginia City Hall ...... 20 Babbitt Municipal Building ...... 21 Silver Bay High School ...... 21 PARTICULATE MATTER SAMPLING...... 21 120 MOUDI II Cascade Impactor ...... 21 Respirable Weight Fraction PM2.5...... 24 Total Filter Sampler (TFS) ...... 24 Substrates and Gravimetric Analysis ...... 25 Sampling Protocol...... 25 Cold Weather Sample Collection ...... 27 DATA REPORTING PROTOCOLS ...... 27 TACONITE PARTICLE SOURCE INDEX ...... 57 DATA ANALYSIS ...... 60 Statistical Analysis ...... 60 PM/TPSI Statistical Analysis ...... 63 DISCUSSION OF BACKGROUND AND COMMUNITY SAMPLING RESULTS ...... 64 Background Locations ...... 64 Ely Fernberg Site ...... 64 Weather Conditions ...... 64 Seasonal Comparison ...... 66 Duluth – NRRI ...... 69 Weather Conditions ...... 69 Seasonal Comparisons ...... 69
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Minneapolis – University of Minnesota Mechanical Engineering Building ...... 73 Weather Conditions ...... 73 Seasonal Comparisons ...... 73 MIR Community Locations ...... 77 Keewatin Elementary School...... 77 Sample Site Location Information ...... 77 Weather Conditions ...... 77 Seasonal Comparisons ...... 83 Local Mine/Plant Activity ...... 86 Hibbing High School ...... 88 Sample Site Location and Weather Conditions ...... 88 Weather Conditions ...... 88 Seasonal Comparisons ...... 95 Local Mine/Plant Activity ...... 97 Virginia City Hall ...... 99 Sample Site Location and Weather Conditions ...... 99 Weather Conditions ...... 99 Seasonal Comparisons ...... 106 Local Mine/Plant Activity ...... 108 Babbitt Municipal Building ...... 110 Sample Site Location and Weather Conditions ...... 110 Weather Conditions ...... 110 Seasonal Comparisons ...... 117 Local Mine/Plant Activity ...... 119 Silver Bay High School ...... 121 Sample Site and Weather Conditions ...... 121 Weather Conditions ...... 121 Seasonal Comparisons ...... 128 Local Mine/Plant Activity ...... 130 INFLUENCES OF PLANT ACTIVITY DISCUSSION ...... 132 SIZE FRACTIONATED PARTICULATE MATTER - REPRESENTATIVE GRAPHS ...... 139 Particulate Matter Mode Comparisons ...... 140 PM Modes Based on Plant Activity ...... 143 Inactive Plants ...... 143 Supplementary ...... 143 Active Plants ...... 143 PM Modes Based on Seasonal Differences ...... 143 Graph Comparisons ...... 144 IN SUMMARY ...... 144 CONCLUSIONS ...... 145 Findings ...... 145 Further work ...... 146 ACKNOWLEDGEMENTS ...... 146 REFERENCES ...... 147
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LIST OF TABLES
Table 1. NAAQS for PM2.5 and PM10 (Source: https://www.epa.gov/criteria-air-pollutants/naaqs- table)...... 4 Table 2. Table of Historical PM NAAQS, and associated footnotes (Source: https://www3.epa.gov/ ttn/naaqs/standards/pm/s_pm_history.html)...... 5 Table 3. Summary of MPCA data from 1999 to 2009...... 12 Table 4. Shapiro-Wilk W test for MPCA raw data and log10 transformed data. Test was conducted in JMP 11...... 12 Table 5. Summary of MPCA data after log10 transformation...... 13 Table 6. Calculation of the number of samples required (using MPCA data) at different confidence levels to get the measurements in the range of 83% to 120% of the population means...... 13 Table 7. Summary of 2009 MPCA and NRRI survey in Virginia at same sampling time period...... 14 Table 8. F-test for equal variance check and t-test results for MPCA and NRRI data comparison using log transformed data...... 14 Table 9. The calculated number of community samples required to gain statistical power using MPCA and NRRI variance data...... 14 Table 10. MOUDI cascade impactor stages, ranges, and PM designations (Monson Geerts et al., 2019a)...... 23 Table 11. Ely Fernberg Site – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%)...... 29 Table 12. Duluth – Natural Resources Research Institute – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%)...... 31 Table 13. Minneapolis – University of Minnesota, Mechanical Engineering Building – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%)...... 34 Table 14. Keewatin Elementary School – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%)...... 36 Table 15. Hibbing High School Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%)...... 38 Table 16. Virginia City Hall – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%)...... 40 Table 17. Babbitt Municipal Building – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%)...... 42 Table 18. Silver Bay High School – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%)...... 46 Table 19. Summary table of average PM concentrations from communities by seasonal MOUDI totals – weight/volume air (µg/m3)...... 49 Table 20. Summary table of average PM concentrations from communities by season, including: 3 PM2.5 fraction – weight/volume air (µg/m ), and PM2.5 representative percent (%) of MOUDI total...... 50 Table 21. Summary table of average PM concentrations from MIR communities by local mine/plant activity MOUDI totals - weight/volume air (µg/m3)...... 51 Table 22. Summary table of average particulate matter concentrations from MIR communities by 3 local mine/plant activity, including: PM2.5 fraction – weight/volume air (µg/m ), and PM2.5 representative percent (%) of MOUDI total...... 52
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Table 23. The Beaufort wind force scale (Royal Meteoroligical Society; https://www.rmets.org/ resource/beaufort-scale). Note that weather vanes do not give adequate wind vectors below 4 miles/hour (~1.8 meters/second). The TPSI developed in this report does not take into account winds less than 4 miles/hour since wind directions cannot be determined using weather vanes such as that on the Davis Weather Station for winds below this speed...... 58 Table 24. Weather conditions at the MIR communities and background sites. Percentages represent the amount of time that the winds at the sampling site were greater than 1.8 meters/second (4 feet/second). The percentage = ((total amount of time - time < 1.8m/s)/total amount of time) x 100%...... 66 Table 25. Results of T-tests comparing the average overall PM data for winter and summer concentrations for all MIR community samples...... 61 Table 26. Mean and p-values from t-test to compare PM values between summer and winter...... 61 Table 27. Summary of mean and standard deviation for overall PM concentrations for MIR communities and Ely background...... 62 Table 28. P-value of t-tests to compare overall PM means between MIR communities and the Ely background site...... 62 Table 29. Mean and p-values from t-test between active and inactive conditions for MIR communities...... 62 Table 30. Overall MIR community Pearson correlations between PM variables and TPSI...... 63 Table 31. Individual MIR community Pearson correlation coefficients and p-values between other PM variables with TPSI...... 64 Table 32. TPSI calculation for Keewatin Elementary School...... 81 Table 33. TPSI calculation for Hibbing High School...... 92 Table 34. TPSI calculation for Virginia City Hall...... 103 Table 35. TPSI calculation for Babbitt Municipal Building...... 114 Table 36. TPSI calculation for Silver Bay High School...... 125 Table 37. Timeline of Mesabi Iron Range taconite processing plant closures...... 133 Table 38. Average concentrations by “Coarse” and “Accumulation” (PM1) modes – MIR community samples by local mine/plant activity: weight/volume air (µg/m3) and percent (%) with (standard deviation)...... 141 Table 39. Average concentrations by “Coarse” and “Accumulation” (PM1) modes – MIR communities and background sites by season in which samples were collected: weight/volume air (µg/m3) and percent (%) with (standard deviation)...... 142
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LIST OF FIGURES
Figure 1. Generalized taconite processing flow diagram (USEPA, 2001)...... 7 Figure 2. Study area sampling locations. MIR community sampling occurred in Keewatin, Hibbing, Virginia, Babbitt, and Silver Bay. Background community sampling took place in Ely, Duluth, and Minneapolis (see left side of figure). Taconite processing plants that were also sampled during the NRRI’s PM characterization studies included Keetac, Hibtac, Minntac, Utac, Minorca, and Northshore (right side of figure)...... 11 Figure 3. Locations of taconite plants and communities on the MIR with respect to the Biwabik Iron Formation (BIF; brown-red color), the geological unit mined for iron on the Mesabi Range. Metamorphic zones 1, 2, 3, and 4 refer to different mineralogical zones associated with the BIF that were identified by French (1968) and further refined by McSwiggen and Morey (2008). These zones indicate the mineralogical changes occurring in the BIF progressing along strike from west to east. Mineralogical changes in zones 3 and 4 were the result of thermal metamorphism of the BIF during intrusion of Duluth Complex-related magmas ~1.1 billion years ago. The mineralogical characteristics of these zones are summarized below the map...... 16 Figure 4. Map of Minnesota’s taconite mining operations. The dashed line demarcates western and eastern MIR taconite operations...... 20 Figure 5. Comparison of all community concentrations by season – MOUDI totals (weight/volume air – µg/m3)...... 53 Figure 6. Comparison of all community concentrations by season – PM2.5 (respirable) fraction of the MOUDI totals (weight/volume air – µg/m3)...... 54 Figure 7. Comparison of community concentration averages by season and location – MOUDI totals [weight/volume air (µg/m3)]...... 55 Figure 8. Comparison of community concentration averages by season and location – PM2.5 fraction of MOUDI total [weight/volume air (µg/m3)]...... 56 Figure 9a-b. Ely Fernberg Site winter season wind and precipitation composites...... 65 Figure 10a-b. Ely Fernberg Site summer season wind and precipitation composites...... 65 Figure 11a-b. Comparison of averaged MOUDI stages from Ely Fernberg Background Site by winter season (3 samples) and summer season (3 samples). Bars = St. Dev...... 67 Figure 12a-b. Duluth – Natural Resources Research Institute winter season wind and precipitation composites...... 70 Figure 13a-b. Duluth – Natural Resources Research Institute summer season wind and precipitation composites...... 70 Figure 14a-b. Comparison of averaged MOUDI stages from Duluth - NRRI Background Site by winter season (7 samples) and summer season (5 samples). Bars = St. Dev...... 71 Figure 15a-b. Minneapolis – University of Minnesota Mech. Eng. Building winter season wind and precipitation composites...... 74 Figure 16a-b. Minneapolis – University of Minnesota Mech. Eng. Building summer season wind and precipitation composites...... 74 Figure 17a-b. Comparison of averaged MOUDI stages from Minneapolis UMN Mech. Eng. Background Site by winter season (3 samples) and summer season (3 samples). Bars = St. Dev...... 75 Figure 18. Air photo of the Keewatin, MN community PM sampling site with respect to the taconite mines and processing facilities...... 78 Figure 19a-b. Keewatin Elementary School inactive local plant wind and precipitation composites...... 79 Figure 20a-b. Keewatin Elementary School active local plant wind and precipitation composites...... 79 Figure 21a-b. Keewatin Elementary School winter season wind and precipitation composites...... 80
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Figure 22a-b. Keewatin Elementary School summer season wind and precipitation composites...... 80 Figure 23. Comparison of TPSI to PM concentrations by sample event at the Keewatin site...... 82 Figure 24a-b. Comparison of averaged MOUDI stages from Keewatin Elementary School Site by winter season (3 samples) and summer season (4 samples). Bars = St. Dev...... 85 Figure 25a-b. Comparison of averaged MOUDI stages from Keewatin Elementary School during local mine/plant Inactivity (6 samples) and Activity (1 sample). Bars = St. Dev...... 87 Figure 26. Air photo of the Hibbing, MN community PM sampling site with respect to the taconite mines and processing facilities...... 89 Figure 27a-b. Hibbing High School inactive local plant wind and precipitation composites...... 90 Figure 28a-b. Hibbing High School active local plant wind and precipitation composites...... 90 Figure 29a-b. Hibbing High School winter season wind and precipitation composites...... 91 Figure 30a-b. Hibbing High School summer season wind and precipitation composites...... 91 Figure 31. Comparison of TPSI to PM concentrations by sample event at the Hibbing site...... 93 Figure 32a-b. Comparison of averaged MOUDI stages from Hibbing High School Site by winter season (4 samples) and summer season (5 samples). Bars = St. Dev...... 96 Figure 33a-b. Comparison of averaged MOUDI stages from Hibbing High School during local mine/plant Inactivity (3 samples) and Activity (6 samples). Bars = St. Dev...... 98 Figure 34. Air photo of the Virginia, MN community PM sampling site with respect to the taconite mines and processing facilities...... 100 Figure 35a-b. Virginia City Hall inactive local plant wind and precipitation composites...... 101 Figure 36a-b. Virginia City Hall active local plant wind and precipitation composites...... 101 Figure 37a-b. Virginia City Hall winter season wind and precipitation composites...... 102 Figure 38a-b. Virginia City Hall summer season wind and precipitation composites...... 102 Figure 39. Comparison of TPSI to PM concentrations by sample event at the Virginia site...... 104 Figure 40a-b. Comparison of averaged MOUDI stages from Virginia City Hall Site by winter season (5 samples) and summer season (5 samples). Bars = St. Dev...... 107 Figure 41a-b. Comparison of averaged MOUDI stages from Virginia City Hall during local mine/plant Inactivity (4 samples) and Activity (6 samples). Bars = St. Dev...... 109 Figure 42. Air photo of the Babbitt, MN community PM sampling site with respect to the taconite mines and processing facilities...... 111 Figure 43a-b. Babbitt Municipal Building inactive local plant wind and precipitation composites...... 112 Figure 44a-b. Babbitt Municipal Building active local plant wind and precipitation composites...... 112 Figure 45a-b. Babbitt Municipal Building winter season wind and precipitation composites...... 113 Figure 46a-b. Babbitt Municipal Building summer season wind and precipitation composites...... 113 Figure 47. Comparison of TPSI to PM concentrations by sample event at the Babbitt site...... 115 Figure 48a-b. Comparison of averaged MOUDI stages from Babbitt Municipal Building Site by winter season (7 samples) and summer season (9 samples). Bars = St. Dev...... 118 Figure 49a-b. Comparison of averaged MOUDI stages from Babbitt Municipal Building during local mine/plant Inactivity (7 samples) and Activity (9 samples). Bars = St. Dev...... 120 Figure 50. Air photo of the Silver Bay, MN community PM sampling site with respect to the taconite mines and processing facilities...... 122 Figure 51a-b. Silver Bay High School inactive local plant wind and precipitation composites...... 123 Figure 52a-b. Silver Bay High School active local plant wind and precipitation composites...... 123 Figure 53a-b. Silver Bay High School winter season wind and precipitation composites...... 124 Figure 54a-b. Silver Bay High School summer season wind and precipitation composites...... 124 Figure 55. Comparison of TPSI to PM concentrations by sample event at the Silver Bay site...... 126 Figure 56a-b. Comparison of averaged MOUDI stages from Silver Bay High School Site by winter season (4 samples) and summer season (9 samples). Bars = St. Dev...... 129
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Figure 57a-b. Comparison of averaged MOUDI stages from Silver Bay High School during local mine/plant Inactivity (7 samples) and Activity (5 samples). Bars = St. Dev...... 131 Figure 58. Comparison of all community samples by local plant inactivity versus activity – MOUDI totals (weight/volume air – µg/m3)...... 134 Figure 59. Comparison of all community samples by local plant activity – PM2.5 (respirable) fraction of MOUDI totals (weight/volume air – µg/m3)...... 135 Figure 60. Comparison of community concentration averages during plant inactivity versus activity – MOUDI totals [weight/volume air (µg/m3)]...... 136 Figure 61. Comparison of community concentration averages during plant inactivity versus activity – 3 PM2.5 fraction (weight/volume air – µg/m )...... 137 Figure 62. Comparison of inactive and active concentration averages by location – Total and PM2.5 (weight/volume air – µg/m3)...... 138
LIST OF PHOTOS Photo 1. 120 MOUDI II cascade impactor...... 22 Photo 2. Total Filter Sampler (TFS)...... 24 Photo 3. Equipment housing with pump tote, omni-direction inlet, and Davis weather station located on the Babbitt Municipal Building rooftop...... 26 Photo 4. Internal setup of MOUDI cascade impactor and TFS sampler. The light bulb(s) is used for heating inside the sampling housing during winter conditions...... 27
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INTRODUCTION The Minnesota Taconite Workers Health Study (MTWHS) was initiated in 2008 and included a multicomponent study to further understand taconite worker health issues on the Mesabi Iron Range (MIR) in northeastern Minnesota. Approximately $4.9 million funding was provided by the Minnesota Legislature to conduct five separate studies related to this initiative, including: . An Occupational Exposure Assessment, conducted by the University of Minnesota School of Public Health (SPH); . A Mortality (Cause of Death) study, conducted by the University of Minnesota SPH; . Incidence studies, conducted by the University of Minnesota SPH; . A Respiratory Survey of Taconite Workers and Spouses, conducted by the University of Minnesota SPH; and . An Environmental Study of Airborne Particulate Matter, conducted by the Natural Resources Research Institute (NRRI) at the University of Minnesota Duluth (UMD).
NRRI’s “Environmental Study of Airborne Particulate Matter” comprises a multi-faceted characterization of size-fractionated airborne particulate matter (PM) from MIR community “rooftop” locations, background sites, and all taconite processing facilities active between 2008 and 2014. Characterization includes gravimetric determinations, chemical characterization, mineralogical characterization, and morphological characterization. This report specifically discusses the methods and gravimetric results of multiple aerosol PM sample collections from five communities located within the MIR, as well as three background locations. The samples were collected between 2008 and 2011.
BACKGROUND Excessive exposures to various varieties of mineral dusts have an association with development of a wide variety of diseases including silicosis, coal workers pneumoconiosis, and asbestosis, lung cancer, and mesothelioma (Plumlee et al., 2006). Mesothelioma is a relatively rare cancer that develops in cells of the mesothelium, the protective lining around many of the internal organs of the body, and is most commonly attributed to exposure to asbestos (Fuhrer and Lazarus, 2011; Pass et al., 2004; Robinson et al., 2005). The Minnesota Department of Health Minnesota Cancer Surveillance System (MDH-MCSS) reported a 73% excess in mesothelioma cases relative to the rest of the state among northeastern Minnesota men between 1988 and 1996 (MDH-MCSS, 1999), causing concern that occupations associated with taconite mining may be fundamentally associated with the disease (Allen et al., 2015). Between 2002 and 2006, age-adjusted mesothelioma incidence amongst non-Hispanic white males was more than double that of the state rate for individuals in northeastern Minnesota, whereas mesothelioma incidence amongst non-Hispanic white females was approximately one-half the statewide rate for individuals in northeastern Minnesota (MDH-MCSS, 2012). An initial finding between 1988 and 2008 by the MDH identified 58 individuals with mesothelioma from an original cohort of 72,000 mine workers (MDH, 2007; 2012). The initial MDH (2007) findings prompted the Minnesota Legislature to approve $4.9 million for the University of Minnesota SPH, University of Minnesota Medical School, and the NRRI to conduct a five-year comprehensive study on the possible cause(s) of this disease affecting taconite workers in northeastern Minnesota. Identifying and characterizing what is in the air in both the communities and taconite plants within the study area is paramount to identifying potential mineral dust(s) and their source(s), either directly or indirectly responsible for the higher than normal incidence of this disease. The NRRI’s role in this study was to conduct a baseline environmental study, with an emphasis on characterizing airborne PM, including elongate mineral particles (EMPs) present in the PM, within five MIR communities, three background sites, and six taconite processing plants. Gravimetric, chemical, mineralogical, and morphological characterization was conducted within the NRRI study. The EMPs targeted in this study
NRRI/RI-2019/30 – Community Gravimetric Analysis 2 comprise mineral particles that are of inhalable, thoracic, or respirable size and have a minimum aspect (length-to-width) ratio of 3:1 (Allen et al., 2015; Hwang et al., 2014; NIOSH, 2011). It is important to note that the characterizations presented by the NRRI in this comprehensive study are merely snapshots of the ambient and micro-environmental concentrations taken within a three-year sampling period from strategic localities. While NRRI’s sampling is demonstrably representative of the environments being studied for purposes of characterization, the sampling methodologies and measurements are not meant to be equivalent with those performed by regulatory sampling, nor are the measurements intended to be used for the purpose of regulatory compliance or for deriving historical exposure estimates. Sample methodology and frequency are discussed in further detail below. Although mesothelioma has been linked primarily to the inhalation of asbestos (Wagner et al., 1960), a comprehensive characterization of the ambient air PM is necessary for understanding all of the variables involved with this disease process. Taconite mining and processing activities in northeastern Minnesota can generate substantial amounts of mineral dust that may have the potential to produce adverse human health effects. This mineral dust—or PM—is made up of small particles that are generally micrometer (i.e., µm or micron) and sub-micrometer in size. In addition to mineral particles, the broader category of PM can also include organic dusts, chemicals, and even liquid droplets (Hinds, 1999). Particle size, mineralogy, morphology, and concentration dictate whether there is potential for adverse health effects (Gunter et al., 2007). Amphibole mineral species that have the potential to occur as asbestiform habit may be associated with increased risks for mesothelioma and other cancers. Amphibole mineralization is known to occur in rocks in northeastern Minnesota (French, 1968; Gunderson and Schwartz, 1962; McSwiggen and Morey, 2008; Wilson et al., 2008). With respect to particle size, the United States Environmental Protection Agency (USEPA) is particularly interested in particles with aerodynamic diameters (Baron and Willeke, 2001) less than 10 µm (equivalent to PM10) because they can enter the human lung and potentially cause health issues. The PM10 can be further broken down into “inhalable coarse particles” that are less than 10 µm and “fine particles” that are less than 2.5 µm (ISO, 1995). The one-micrometer size (1 µm, PM1) is generally accepted as the distinction between the coarser dusts generated through mineral comminution processes and PM resulting from combustion (Hinds, 1999). Health effects from exposure to “fine” PM can lead to a variety of pulmonary and cardiovascular problems, including multiple types of cancer, when asbestiform particles are involved (Gunter et al., 2007). Reports from this study discuss the findings of airborne PM sampling in the MIR communities, background locations, and taconite plants. Companion reports are also available and include: Development of Standard Operating Procedures (SOP) for Particle Collection and Gravimetric Analysis (Monson Geerts et al., 2019a); Taconite Processing Facilities Particulate Matter Collection and Gravimetric Analysis (Monson Geerts et al., 2019b); A Characterization of the Mineral Component of the Particulate Matter (Monson Geerts et al., 2019c); and Elemental Chemistry of the Particulate Matter (Monson Geerts et al., 2019d). In addition, a report focusing on the collection and analysis of EMPs in age-dated lake sediments on the MIR (Zanko et al., 2019) is also available.
What is Mesothelioma? The aggressive type of cancer known as mesothelioma is rare and most commonly results from malignancy of mesothelial cells of the pleural (outer lung lining) and peritoneal (abdominal cavity lining) tissues (Fuhrer and Lazarus, 2011). The disease is nearly always fatal and has been linked to the exposure of asbestos and other mineral fibers (via inhalation) (IOM, 2006; NIOSH, 2011; Robinson et al., 2005; Wagner et al., 1960). Following diagnosis, median survival is commonly 9 to 12 months. Male rates for mesothelioma are considerably higher than female rates, and rates of the disease are higher in industrialized countries relative to non-industrialized countries (Robinson et al., 2005, and references therein).
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While there is much debate and research on the specific minerals that may be responsible for mesothelioma, recommendations by the National Institute for Occupational Safety and Health (NIOSH) have resulted in regulations through other government agencies concerning six minerals as described in the description of a “covered” mineral below: “NIOSH considers asbestos to be a “Potential Occupational Carcinogen”* and recommends that exposure be reduced to the lowest feasible concentration. The NIOSH recommended exposure limit (REL) for airborne asbestos fibers and regulated EMPs is 0.1 countable EMP from one or more covered minerals per cubic centimeter, averaged over 100 minutes, where: . a “Countable” elongate mineral particle (EMP) is any fiber or fragment of a mineral longer than 5 µm with a minimum aspect ratio of 3:1 when viewed microscopically with use of NIOSH Analytical Method 7400 (“A” rules) or its equivalent; and . a “Covered” mineral is any mineral having the crystal structure and elemental composition of one of the asbestos varieties (chrysotile, riebeckite asbestos [crocidolite], cummingtonite-grunerite asbestos [amosite], anthophyllite asbestos, tremolite asbestos, and actinolite asbestos) or one their nonasbestiform analogues (the serpentine minerals antigorite and lizardite, and the amphibole minerals contained in the cummingtonite- grunerite mineral series, the tremolite-ferroactinolite mineral series, and the glaucophane-riebeckite mineral series). This clarification of the NIOSH REL for airborne asbestos fibers and related EMPs results in no change in counts made, as defined by NIOSH Method 7400 (‘A’ rules). However, it clarifies definitionally that EMPs included in the count are not necessarily asbestos fibers” (NIOSH, 2011).
Other minerals have been documented to date for which exposure to have been linked to mesothelioma, although these minerals are not currently regulated. They include, but are not limited to, the following: winchite and richterite – two amphiboles indicated in Libby, MT study cases (Gunter et al., 2007; Wylie and Verkouteren, 2000), balangeroite (Compagnoni et al., 1983; Turci et al., 2009), and erionite (a zeolite mineral: Carbone et al., 2011; NTP, 2014; Wagner et al., 1985). Recent meta-analysis of epidemiological data suggests different toxicities exist, depending on mineral type and dimensions (Berman and Crump, 2008; P. Cook, USEPA, 2010 pers. comm.). However, due to past confusion in the research over mineralogical, morphological, and dimensional details surrounding possible causes of disease, NIOSH developed its Roadmap publication (2011) as a strategy for facilitating future research. One component of the NIOSH Roadmap expanded the definition of “asbestos” to include both asbestos fibers and all other related morphologies, including cleavage fragments, in their recommended exposure limits (REL). This action was done primarily to facilitate research to better understand the mineralogical, morphological, and dimensional details in predicting asbestos-related disease as well as reduce exposures to the lowest feasible concentrations. Due to the difficulties of applying current descriptive terminology to PM of micrometer scale (e.g., the mineralogical definition of asbestiform, which Gunter et al. (2007) state should be reserved for amphiboles that split lengthwise), the NRRI’s study will refer to all particles with an aspect ratio ≥ 3:1 as EMPs. See also Appendix G (glossary) of the SOP report (Monson Geerts et al., 2019a).
REGULATION CONCERNING PARTICULATE MATTER (PM) It is important to briefly outline the history and development of regulations regarding PM in the United States. The Clean Air Act, which was amended in 1990, requires the USEPA to set National Ambient Air Quality Standards (NAAQS) for a variety of pollutants considered harmful to human health
*NIOSH’s use of the term “Potential Occupational Carcinogen” dates to the OSHA classification outlined in 29 CFR 1990.103 and, unlike other agencies, is the only classification for carcinogens that NIOSH uses (OSHA, 1990).
NRRI/RI-2019/30 – Community Gravimetric Analysis 4 and the environment, including PM. Original USEPA regulations were created for PM with diameter less than 10 µm (PM10). As the USEPA states, “The Clean Air Act identifies two types of national ambient air quality standards. Primary standards provide public health protection, including protecting the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.” (https://www.epa.gov/criteria-air-pollutants/naaqs-table) The Minnesota Pollution Control Agency (MPCA) has summarized the Clean Air Act regulation of particulate matter as follows (https://www.pca.state.mn.us/air/fine-particle-pollution): “The Clean Air Act regulates two sizes of particulate matter: PM2.5 (fine particles) and PM10. PM2.5 includes particulate matter that is less than 2.5 microns in diameter; PM10 includes all particulate matter less than 10 microns in diameter (including PM2.5). The USEPA sets National Ambient Air Quality Standards (NAAQS) for both PM2.5 and PM10, including both primary standards to protect public health and secondary standards to protect the environment. In 2012, the USEPA reviewed the science related to the health and environmental impacts of particulate matter and revised the NAAQS to reflect the most up-to-date information. The level 3 of the current primary and secondary daily fine particle [PM2.5] standard is 35 µg/m and the 3 primary annual standard is 12 µg/m . The primary and secondary daily PM10 standard is 150 µg/m3.”
The USEPA’s NAAQS standards for PM2.5 and PM10 are summarized in Table 1.
Table 1. NAAQS for PM2.5 and PM10 (Source: https://www.epa.gov/criteria-air-pollutants/naaqs-table). Primary/ Averaging Pollutant Level Form Secondary Time primary 1 year 12.0 µg/m3 Annual mean, averaged over 3 years
secondary 1 year 15.0 µg/m3 Annual mean, averaged over 3 years Particle PM2.5 primary and Pollution 24 hours 35 µg/m3 98th percentile, averaged over 3 years (PM) secondary
primary and 3 Not to be exceeded more than once PM10 24 hours 150 µg/m secondary per year on average over 3 years
As Table 2 shows, the PM2.5 and PM10 standards have evolved over time. The EPA revoked the 3 3 annual PM10 NAAQS in 2006 (which had been 50 µg/m ), so only the 24-hour standard of 150 µg/m currently applies, and is not to be exceeded more than once per year on average over a three-year period (USEPA, 2013).
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Table 2. Table of Historical PM NAAQS, and associated footnotes (Source: https://www3.epa.gov/ttn/ naaqs/standards/pm/s_pm_history.html).
(1) Units of measure are micrograms per cubic meter of air (µg/m3). (2) TSP = total suspended particles. (3)The level of the annual standard is defined to one decimal place (i.e., 15.0 µg/m3) as determined by rounding. For example, a 3-year average annual mean of 15.04 µg/m3 would round to 15.0 µg/m3 and thus meet the annual standard, and a 3-year average of 15.05 µg/m3 would round to 15.1 µg/m3 and, hence, violate the annual standard (40 CFR part 50 Appendix N). (4)The level of the standard was to be compared to measurements made at sites that represent “community-wide air quality” recording the highest level, or, if specific requirements were satisfied, to average measurements from multiple community-wide air quality monitoring sites (“spatial averaging”). (5) See 69 FR 45592, July 30, 2004. (6) The level of the 24-hour standard is defined as an integer (zero decimal places) as determined by rounding. For example, a 3-year average 98th percentile concentration of 35.49 µg/m3 would round to 35 µg/m3 and thus meet the 24-hour standard and a 3-year average of 35.50 µg/m3 would round to 36 and, hence, violate the 24-hour standard (40 CFR part 50 Appendix N). (7) The EPA tightened the constraints on the spatial averaging criteria by further limiting the conditions under which some areas may average measurements from multiple community-oriented monitors to determine compliance (see 71 FR 61165-61167). (8) The EPA revoked the annual PM10 NAAQS in 2006.
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For workplace indoor air quality, the Occupational Safety and Health Administration (OSHA) enforces air quality regulations. For workplace indoor air quality at mining operations and mineral processing facilities, the Mine Safety and Health Administration (MSHA) enforces air quality regulations. Without specificity to the mineralogy of the PM, the overall weight (OSHA – total dust 15 mg/m3 and 3 PM10 5 mg/m ) per volume air can be compared with exposure limits set by federal regulators. Typically, these exposure limits are expressed as eight-hour time-weighted averages. For example, OSHA has a permissible exposure limit (PEL) regulation regarding general PM other than coal, silica, or asbestos, which is directed at respirable particles less than 10 µm in size that are not otherwise regulated, of 5,000 µg/m3 (5 mg/m3). The American Conference of Governmental Industrial Hygienists (ACGIH) 2001 TLV® (threshold limit value; ACGIH, 2001) recommends a limit of 3,000 µg/m3 (3 mg/m3) for PM. In general, MSHA has adopted the regulations set by OSHA 1910.1000 Limits for Air Contaminants (OHSA, 1997). Keep in mind that these limits and/or recommendations decrease with an increase in the percent of silica (SiO2) content and/or the presence of asbestos fibers, both of which are separately regulated based on specific analytical methods. This may be an issue in certain areas of Minnesota’s taconite processing facilities, depending on the overall mineralogy of the rocks being mined, and the mineral processing that takes place to produce the taconite pellets (see generalized process flow diagrams – Fig. 1, USEPA, 2001; 2003). For instance, crushing operations are likely to have higher silica concentrations than other process operations because the dust generated during this process is from the raw, silica-containing ore prior to magnetic separation and associated magnetic iron concentration. Magnetic separation removes the magnetic iron oxide ore minerals (primarily magnetite; Fe3O4) from other non-magnetic gangue minerals contained in the ore. This process is wet and is likely to generate low concentrations of silica dust. During agglomeration, a clay component (bentonite, which is an aluminum phyllosilicate) is added to the iron oxide concentrate to make “green balls,” which are unfired taconite pellets. There may also be increased amounts of silica in areas such as the agglomerators/balling drums because of this clay addition. Limestone containing calcite (CaCO3) and/or dolostone containing dolomite (Ca,Mg(CO3)2) may also be added during the production of flux pellets; therefore, dusts containing carbonate minerals may also be present in the agglomerator/balling drum areas. In the vicinity of the kiln/pellet discharge, silica dust may also be present as a result of liberation of silica from the taconite pellets during movement within and immediately after heating in the kiln (Fig. 1).
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Figure 1. Generalized taconite processing flow diagram (USEPA, 2001).
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Figure 1 (continued).
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OBJECTIVES In response to the Minnesota Legislature bill H.F. 3569 (Minnesota Legislature, 2008), the University of Minnesota SPH and the NRRI at UMD conducted a multi-component study (the MTWHS) related to physical, mineralogical, and chemical attributes of mineral dust (NRRI) and taconite workers’ health (University of Minnesota SPH) based on specific attributes of mineral dust present in industrial and public settings on Minnesota’s MIR. NRRI’s role in the MTWHS includes measurement and characterization of airborne PM in the MIR communities, taconite processing plants, and background locations. Although the emphasis of the research is focused on possible links to the elevated number of cases of mesothelioma and other cancers in taconite workers (Allen, 2014; Allen et al., 2015; Lambert et al., 2013; MDH, 2007; MDH-MCSS, 1999; MDH-MCSS, 2012), it is imperative that a comprehensive characterization of the PM in both community and plant environments be conducted. A comprehensive characterization (concentrations, morphological characteristics, mineralogical attributes, and chemical compositions), as well as identification of possible sources of ambient PM in the communities and plants, may provide important data to increase our understanding of air quality as related to PM on the MIR and may aid in developing means to address overall air quality. Although specific concentrations of PM have not been associated with or linked to mesothelioma, this component of the comprehensive characterization of the ambient PM on the MIR will be addressed. This report discusses the gravimetric characteristics, including concentrations of PM within the five MIR communities and three background locations.
Questions to be addressed . How much PM is present in the ambient air of each of the five MIR communities? Furthermore, do PM concentrations vary by season or local mine/plant activity? How do these PM levels compare to those at background locations? . Are PM levels in the MIR communities greater when the prevailing wind is blowing from a direction that contains potential mine/plant sources relative to wind directions that do not encounter mine/plant sources? . What are the concentrations of the various size distributions of PM in these locations? Furthermore, do the size distributions of PM vary by season or local mine/plant activity? How do the size distributions compare to those at background locations? . Are PM concentrations and size distributions constant across the MIR? If not, can any of these differences be explained by the geology of the region? . What information can be gained by using a sampler that provides size-fractionated PM data (MOUDI) relative to high volume samplers typically utilized for community air monitoring? Can the percent fraction of PM tell us anything? . What further work is warranted as a follow-up to this study component?
To address the general question “What is in the air?”, the NRRI has conducted a multifaceted sampling program involving both: 1) size-fractionated PM sampling; and 2) total filter sampling at each sampling location. Size-fractionated PM sampling allows for the determination and evaluation of various PM designations and was completed using a Micro-Orifice Uniform Deposit Impactor (MOUDI) II Model 120 sampler (Marple et al., 1991; 2014). This 10-stage cascade impactor sorted the PM with respect to nominal aerodynamic diameter cut sizes of: 10 µm, 5.6 µm, 3.16 µm, 1.8 µm, 1.0 µm, 0.56 µm, 0.32 µm, 0.18 µm, 0.10 µm, and 0.056 µm, plus an initial cut of 18 µm, and an after-filter below the impaction stages that collected material with an aerodynamic diameter less than 0.056 µm. This comprehensive type of sampling allowed for the calculation (and graphical depiction) of particle mass concentrations by size and long-term averages by stage, as well as for different aerodynamic diameter particles. The MOUDI provided the study with a degree of size and gravimetric detail that would not be possible using more conventional PM samplers.
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SAMPLING METHODOLOGY The emphasis of this study was on the characterization of EMPs within the collected PM; however, a comprehensive characterization of the PM was also essential. Specific objectives associated with the aerosol sampling of PM and characterization included: 1) gravimetric analysis of PM and comparisons between communities and background locations; 2) comparisons of PM concentration in the communities based on local mine/plant activity (active or inactive); 3) comparisons related to the seasons in which the particulate matter was collected; and 4) comparisons of PM concentrations and characteristics across the MIR with respect to their geographic location and local geology. Sample locations for the study included five population centers on the MIR (including west and east iron range communities), as well as three separate background locations. Sampling was opportunistic with respect to location, focusing on populated areas rather than sampling sites based on a grid system. The highest priority populated areas included the towns located nearest the taconite operations, which comprised open pit mines and taconite processing plants. In addition, secured access to the rooftops of public buildings near city centers was utilized at the following locations: Keewatin (elementary school), Hibbing (high school), Virginia (city hall), Babbitt (municipal building) and Silver Bay (high school). Secured rooftop sampling locations were also utilized at the Duluth (NRRI rooftop) and Minneapolis (Mechanical Engineering Building on the University of Minnesota campus) background sites. A third background site near Ely, Minnesota (Ely Fernberg site) utilized already established remote air sampling infrastructure (Fig. 2).
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Sampling Locations
Figure 2. Study area sampling locations. MIR community sampling occurred in Keewatin, Hibbing, Virginia, Babbitt, and Silver Bay. Background community sampling took place in Ely, Duluth, and Minneapolis (see left side of figure). Taconite processing plants that were also sampled during the NRRI’s PM characterization studies included Keetac, Hibtac, Minntac, Utac, Minorca, and Northshore (right side of figure).
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Preliminary Statistical Analysis Statistical analysis was performed early in the study to calculate the minimum number of both community and background samples required to accurately and statistically characterize ambient PM concentrations. Ambient aerosol data that was collected by the Minnesota Pollution Control Agency (MPCA) for the determination of Total Suspended Particulate Matter (TSP), PM10, and PM2.5 in Virginia, MN between 1999 and 2009 (Table 3) was used to project the number of samples needed to determine long-term averages for PM on the MIR. The normal distributions of these data were tested using a Shapiro-Wilk W Test in the software program JMP 11 (JMP, 2014). The null hypothesis of Wilk W test is H0: the data are from normal distribution. A small p-value will reject this null hypothesis and indicate a non-normal distribution.
Table 3. Summary of MPCA data from 1999 to 2009. Std Particles Median Mean Std Dev Min Max N Rows Count* Dates Error 05/30/1999- PM2.5 5.2 6.445 4.413 0.6 36 0.153 917 832 04/25/2009 12/14/1999- PM10 13.28 15.175 8.116 3.232 72.48 0.353 564 528 07/12/2009 12/14/1999- TSP 31.42 35.389 19.203 4.173 125.4 0.828 564 538 07/12/2009 *Count represents the rows without missing data.
Results from Table 4 show that the raw MPCA data did not have normal distribution, but the log10 transformed data are either normally distributed or close to normally distributed. Therefore, a log10 transformation has been applied to the data to perform further analysis (Table 5). The sample size can be determined by the following equation (Eq. 1):
= / (Eq. 1) �� 2� 2 � � �̅−� � Here, n represents sample size, / is the z value based on confidence level ɑ, is the standard deviation, μ is the population mean and is the mean of future measurement. The Z value can be � 2 obtained using the Z table: for 95%� confidence, Z = 1.96; for 90% confidence, Z=1.645;� for 80% confidence, Z=1.28. �̅
Table 4. Shapiro-Wilk W test for MPCA raw data and log10 transformed data. Test was conducted in JMP 11.
Raw data, no transformation Log10 transformed Shapiro-Wilk W p-value Shapiro-Wilk W p-value PM2.5 0.809619 <0.0001 0.993862 0.0018 PM10 0.871565 <0.0001 0.998723 0.9725 TSP 0.919154 <0.0001 0.991121 0.0026
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Table 5. Summary of MPCA data after log10 transformation. Std Particles Median Mean Std Dev Min Max N Rows Count* Dates Error 05/30/1999- PM2.5 0.716 0.728 0.263 -0.222 1.556 0.009 917 832 04/25/2009 12/14/1999- PM10 1.123 1.127 0.216 0.509 1.860 0.009 564 528 07/12/2009 12/14/1999- TSP 1.497 1.486 0.242 0.620 2.098 0.010 564 538 07/12/2009
An acceptable deviation from the population mean is 20%, so = [80% × μ, 120% × μ]. It should be noted that log transformed data is used, so log = [log μ -0.0969, log μ + 0.0792]. This range shows an uneven distribution of log around log μ. It is impossible to compute�̅ sample size with uneven range, so it is assumed one balanced range for log . To guarantee�̅ future data will fall in the range of 20% deviation from population,�̅ the l log range is narrowed to be [log μ -0.0792, log μ + 0.0792]; in other words, = [83% × μ, 120% × μ]. Therefore,�̅ log – log μ|=0.0792. Standard deviations are identified in Table 5. Using the Table 5 data and �̅different Z values at a different confidence level, sample size based on the MPCA�̅ data can be computed and is presented�̅ in Table 6. Based on the PM variance data from Virginia, a minimum of 13 samples would be needed to determine mean PM10 ±20% at 80% confidence level, and 16 and 19 samples would be needed to determine mean TSP and PM2.5 ±20% at 80% confidence level, respectively.
Table 6. Calculation of the number of samples required (using MPCA data) at different confidence levels to get the measurements in the range of 83% to 120% of the population means. 95% confidence, 90% confidence, 80% confidence, Standard Deviation Z = 1.96 Z = 1.645 Z = 1.28 PM2.5 0.263 43 30 19
PM10 0.216 29 21 13 TSP 0.242 36 26 16
As is now known, the data before log transformation demonstrated large skewness. The log transformed data have been used to calculate a t-test to compare if there is a significant difference between the MPCA and NRRI data (Table 7). There are two types of t-tests: one assumes equal variance and the other assumes unequal variance. The F-test was used first to check whether or not the variance between MPCA and NRRI data are equal. After that, an appropriate t-test was used. The null hypothesis of t-test H0 was: no significant difference, = . A small p-value will reject this hypothesis. This comparison was also conducted in JMP. 1 2 �̅ �̅
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Table 7. Summary of 2009 MPCA and NRRI survey in Virginia at same sampling time period. Agency Variable Mean Std Dev Min Max Std Err Median N Raw data
MPCA PM2.5 6.192 4.584 1.4 22.8 0.899 4.85 26
MPCA PM10 11.694 6.698 3.764 32.56 1.087 10.605 38 MPCA TSP 30.356 15.855 7.143 76.19 2.539 30.03 39
NRRI PM2.5 7.042 2.234 4.06 11.24 0.706 7.26 10
NRRI PM10 9.929 3.005 5.83 15.06 0.950 10.59 10 NRRI MOUDI-T 12.700 3.753 7.017 18.008 1.187 13.309 10
Log10 transformed
MPCA PM2.5 0.697 0.294 0.146 1.358 0.058 0.686 26
MPCA PM10 1.009 0.226 0.576 1.513 0.037 1.025 38 MPCA TSP 1.416 0.256 0.854 1.882 0.041 1.478 39
NRRI PM2.5 0.827 0.143 0.609 1.051 0.045 0.860 10
NRRI PM10 0.977 0.140 0.766 1.178 0.044 1.025 10 NRRI MOUDI-T 1.084 0.142 0.846 1.255 0.045 1.124 10
Table 6 gives the number of samples required to satisfy different confidence levels. At minimum, 13 samples are required. However, we should note that the NRRI sampled in continuous 120- to 168-hour time periods, while MPCA sampled in a 24-hour time period. The longer sampling time period can reduce data variability, as shown in Table 7, where NRRI’s data have smaller standard deviation than MPCA’s data, and this difference is significant per the F-test (Table 8). In this case, the MPCA’s standard deviation was used in the calculation, but it may overestimate the number of samples required. Therefore, in conclusion, the NRRI’s standard deviation was used to represent population variance in Eq. 1 to recalculate the number of samples required to obtain statistical power (Table 9).
Table 8. F-test for equal variance check and t-test results for MPCA and NRRI data comparison using log transformed data. p-value p-value from t-test Variable Conclusion from F-test Conclusion from F-test with Unequal Variance PM2.5 0.0296 Unequal variance 0.4629 No significant difference PM10 0.0150 Unequal variance 0.2299 No significant difference TSP <0.0001 Unequal variance <0.0001 Significant difference
Table 9. The calculated number of community samples required to gain statistical power using MPCA and NRRI variance data.
Standard Deviation 95% confidence, 90% confidence, 80% confidence, (NRRI data) Z = 1.96 Z = 1.645 Z = 1.28 PM2.5 0.143 13 9 5
PM10 0.140 13 9 5 TSP/MOUDI-T 0.142 13 9 5
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Using the summary PM data in Table 7 was also useful in comparing PM2.5 and PM10 from two separate sources, collected during the same year and location by different sampling devices, where no significant difference was determined. Significant difference was, however, present between the MPCA’s TSP and the NRRI’s MOUDI total during this same period. It should be noted that it was assumed NRRI’s standard deviation was a population standard deviation in the calculation. The number in Table 8 may not be as accurate, but it provides some reference information. In addition, NRRI’s MOUDI total was significantly different from MPCA’s TSP (Table 8), so the number of samples for total PM measurement is not applicable. Based on the following recommendations, historical data, and limitations, including 1): advice from NRRI’s Scientific Advisory Board (Berman et al., 2008); 2) guidance from particle scientist collaborators Dr. Virgil Marple (University of Minnesota) and Dr. Dale Lundgren (University of Florida); 3) historical long-term averages of MPCA PM monitoring in MIR communities; 4) variability of MPCA EMP analyses from Babbitt, MN; 5) a phased approach by comparing early NRRI PM and EMP analyses to the above averages and variability; and 6) limitations due to overall budget, a characterization sampling plan was devised that included a minimum of three (120- to 168-hour) ambient PM samples from winter season (November–April) and a minimum of three ambient PM samples from summer season (May–October), with additional samples added from either season based on periods of inactivity of the local taconite mines/plants.
STUDY AREA As Figure 2 shows, this community study was geographically extensive. The geographic footprint of the study area stretched over 100 miles from the westernmost MIR taconite mining operations and communities to the easternmost, while the study’s background collection sites were separated by 250 miles from north to south. The taconite mining companies and their corresponding processing facilities that also participated in this study are shown in Figure 2 (right) and depicted in Figure 3 with respect to geographical reference and proximity to the Duluth Complex. The geology of the iron-formation changes at the east end of the MIR due to thermal metamorphism associated with the intrusion of the Duluth Complex approximately 1.1 billion years ago (Fig. 3; French, 1968; McSwiggen and Morey, 2008). Thermal metamorphism is known to cause grain size changes in rocks (generally coarser grained in rocks with higher degrees of thermal metamorphism), which may result in differences in PM concentrations and particle size PM fractional percentages when subjected to comminution practices. Therefore, the proposed sample events were increased to a minimum of 12 samples each for the communities of Babbitt and Silver Bay. These two MIR communities occur within the zones of the highest grade of thermal metamorphism in the Biwabik Iron Formation (BIF). Mineralogical changes in these most thermally metamorphosed zones led to the local development of amphibole bearing mineral assemblages (French, 1968; McSwiggen and Morey, 2008). The five MIR communities in northeastern Minnesota include, from west to east, Keewatin, Hibbing, Virginia, Babbitt, and Silver Bay (refer to Fig. 2, left). These communities were chosen for their spatial distribution across the 110-mile-long MIR, their relevance as population centers, their proximity to the six taconite processing plants, and the geological attributes of the BIF, the source of the taconite ores mined in northeastern Minnesota. In conjunction with the sampling at MIR communities, aerosol PM samples were also collected from three background sites including: Ely (rural and north of the MIR), Duluth (mid-sized city and south of the MIR), and Minneapolis (large metropolitan/industrial area not in NE MN) (Fig. 2, left). All five MIR communities and background sites were sampled at least three times during both summer season (defined as May through October) and winter season (defined as November through April).
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Biwabik Iron Formation Mineralogy West to East
Zones 1 and 2: quartz, magnetite, Zones 3 and 4: quartz, magnetite, grunerite, hematite, carbonates, talc, chamosite, hornblende, hedenbergite, ferrohypersthene greenalite, minnesotaite and stilpnomelane (ferrosilite), and fayalite
Figure 3. Locations of taconite plants and communities on the MIR with respect to the Biwabik Iron Formation (BIF; brown-red color), the geological unit mined for iron on the Mesabi Range. Metamorphic zones 1, 2, 3, and 4 refer to different mineralogical zones associated with the BIF that were identified by French (1968) and further refined by McSwiggen and Morey (2008). These zones indicate the mineralogical changes occurring in the BIF progressing along strike from west to east. Mineralogical changes in zones 3 and 4 were the result of thermal metamorphism of the BIF during intrusion of Duluth Complex-related magmas ~1.1 billion years ago. The mineralogical characteristics of these zones are summarized below the map.
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To be clear, the study was not conceived to conduct sampling of a sufficient density to achieve the spatial and temporal variation of PM properties in the communities studied; this was not the study’s objective, nor was its budget large enough to conduct an undertaking of that magnitude. The study was designed, given the resources available, to quantify and characterize airborne PM present in the communities of the MIR, to address the fundamental question asked prior to the study’s start: “What is in the air?”
Regional Geology The MIR is approximately 120 miles long and averages up to two miles in width. Rocks that make up this range comprise the Paleoproterozoic Animikie Group, which is composed of three major geological formations. These formations include: 1) the Pokegama Formation (also known as the Pokegama Quartzite), which comprises an upper member of orthoquartzite, a middle member of interbedded siltstone and shale, and a lower member of shale with interbedded siltstone; 2) the BIF, a 175- to 300- foot-thick sequence of iron-rich sedimentary rocks that has historically been subdivided into four informal members including, from bottom to top, the Lower Cherty Member, the Lower Slaty Member, the Upper Cherty Member, and the Upper Slaty Member; and 3) the Virginia Formation, a sequence of argillite, sandstone, and graywackes at least 600 feet thick that makes up the top of the Animikie Group. These three formations generally strike in a northeast-southwest direction, but locally, strikes oriented south-southwest to north-northeast occur in the vicinity of the Virginia Horn (Fig. 3). On the MIR, these three formations typically have relatively shallow dips, ranging from 3 to 15 degrees, with the steepest dips occurring in the easternmost MIR adjacent to the Duluth Complex (Severson, 2012). Southwick et al. (1988) and Ojakangas (1994) suggest that the Animikie Group sedimentary strata were deposited in a continental shelf environment in a shallow sea that formed in a northward-migrating foreland basin that developed in response to compressional tectonic activity to the south during the Penokean Orogeny (1880–1830 Ma; Schulz and Cannon, 2007). To the east, the Animikie Group sedimentary strata are in contact with the Duluth Complex, which is composed of a series of mafic (iron- and magnesium-rich igneous rocks containing 45%–52% SiO2 (LeBas et al., 1986; LeBas and Streckeisen, 1991)) and locally ultramafic igneous intrusive rocks (generally magnesium-rich igneous rocks containing less than 45% SiO2 (LeBas et al., 1986; LeBas and Streckeisen, 1991)). Details regarding the specific intrusions and rock types that comprise the Duluth Complex can be found in Miller et al. (2002). The ~1.1-billion-year-old Duluth Complex provided heat that resulted in local thermal metamorphism of the BIF, altering its mineral, chemical, and physical characteristics (French, 1968; McSwiggen and Morey, 2008; Severson et al., 2009). The mineralogy of the BIF is an important underlying control on the composition of the dust produced at MIR taconite operations. Although stratigraphic units were initially named and identified locally in different geographic regions of the MIR, the submembers of the BIF being mined were correlated and are, for the most part, mineralogically redundant across the western three-quarters of the MIR (Severson et al., 2009). However, mineral changes first begin to occur locally in the eastern quarter of the BIF as a result of contact (thermal) metamorphism (Severson, 2012). These mineralogical changes occurred 1.1 billion years ago during the emplacement collectively known as the Duluth Complex. Heat associated with this event raised the temperature of the BIF, with the easternmost parts of the BIF attaining the highest temperatures. The thermal metamorphism of French’s eastern Zones 3 and 4 (French, 1968) caused primary iron-formation minerals to react to locally form new suites of iron-rich amphiboles and pyroxenes, whereas the iron- rich phyllosilicate minerals in Zones 1 and 2 (i.e., stilpnomelane, minnesotaite, greenalite, etc.) were unaffected. As stated by McSwiggen and Morey (2008): “Most of the Biwabik Iron Formation has not been metamorphosed to any extent and contains mineral assemblages indicative of low-grade diagenetic processes (Morey, 2003).” The amphiboles of Zones 3 and 4 are principally of the cummingtonite-grunerite series along with actinolite and hornblende (French, 1968; Ross et al., 1993).
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Mineralogy, morphology, and EMP dimensions are discussed in greater detail below and in Monson Geerts et al. (2019c). In Figure 3, the brownish-red-colored geological unit is the BIF, the geological unit that is the source of the iron ore mined on the Mesabi Range. Metamorphic zones 1, 2, 3, and 4 refer to different mineralogical zones associated with the BIF that were identified by French (1968) and further refined by McSwiggen and Morey (2008). These zones identify distinct mineral assemblages that occur in the BIF along strike from west to east. As described previously, these distinct mineral assemblages resulted from thermal metamorphism of the BIF by the intrusion of Duluth Complex-related magmas approximately 1.1 billion years ago (French, 1968; McSwiggen and Morey, 2008; and others). The mineralogy of the different zones reflects occurrences of amphiboles towards the contact with the intrusive rocks that have been identified in Zones 3 and 4 (Fig. 3; French, 1968; McSwiggen and Morey, 2008).
Taconite Mines and Processing Plants In general, the processes within the six taconite ore processing plants in northeast Minnesota are essentially the same (Zanko et al., 2007; 2010), although minor differences may be present in specific processes and equipment used. These differences mostly reflect the age of specific plants. Particulate matter emissions within these plants may vary substantially and are directly related to—and change with respect to—the location within the ore process sequence. Particulate matter levels within the plants are controlled by a variety of devices, including, but not limited to: cyclones, multi/rotoclones, wet scrubbers, bag houses, electrostatic precipitators, and water sprays. According to the USEPA (1997), the largest source of PM emissions in taconite ore mines comes from traffic on unpaved haul roads. Wind erosion on unpaved road surfaces and non-vegetated waste rock and tailings basins can also contribute substantial amounts of PM emission at taconite mines. The USEPA also states that although blasting is a notable source of the various size fractions of PM, it is a short-term event, and most materials settle quickly (Richards and Brozell, 2001; USEPA, 1997). Upon observing and evaluating a taconite mine blast, the NRRI and its aerosol science advisors agreed that given the number of variables related to meteorological conditions, sampling logistics, and the short-lived nature of the dust plume, an attempt to characterize a blast would be difficult to perform and would be of limited use to this study. This conclusion is consistent with, and supported by, USEPA’s own approach of screening out/removing anomalous PM data (what is referred to as "exceptional-type events" or "exceptional events") when calculating "background" PM concentrations (USEPA, 1997; 2016). Doubtless, “exceptional-type events” (including blasting) will and did occur during community sampling events. However, no attempt has been made to look for, or screen out, such episodic events; the collected data have been used in their entirety (i.e., “as-is”) and include all potential inputs. There is no doubt that mining activities in northeastern Minnesota have, to at least some degree, an influence on PM emissions in the community centers surrounding the mines and their associated taconite processing facilities. The NRRI’s role in this study has been to characterize the PM emissions in both the processing plants (see Monson Geerts et al., 2019b) and adjacent communities, so that the information exists to answer the fundamental question “What is in the air?”
Background (Community) Sampling Sites As mentioned briefly above, two background community sampling sites were initially chosen so that aerosol PM could be obtained without the influences of local taconite mining and/or processing. Due to primarily westerly prevailing winds, site selection was based on relative proximity and locations north and south of the MIR. The sites of Ely, Minnesota and Duluth, Minnesota were chosen, primarily based on this reasoning. As well, the Ely Fernberg Site was and continues to be a well-established regulatory air monitoring site.
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Ely Fernberg Site The Ely Fernberg Site (NAD 83 UTM North 612338 easting, 5311442 northing, elevation 1709’) is the northernmost-located community background sampling site. It is the only air monitoring site of the eight community/background sites that is not located on a rooftop. The site is located approximately 18 miles east of the town of Ely on State Highway 169 (Fernberg Trail), just inside the boundary of Lake County. Ely has a population of approximately 3,500 residents. The site sits atop a geographical high to the south of the highway at an elevation of 1,700 feet. The location is characterized by a clearing with numerous meteorological and other PM monitoring devices (extensive historical data by various state agencies) and is wired with electrical power and secured with an access gate.
Duluth – Natural Resources Research Institute (NRRI) Just as the Ely Fernberg Site serves as a background location north of the MIR, Duluth (NAD 83 UTM North 560440 easting, 5187236 northing, elevation 1495’) was chosen as a background aerosol sampling location to the south. This background community sampling site is located on the six-story rooftop of the University of Minnesota Duluth’s NRRI facility, which is located north of the city of Duluth on US Highway 53 (street address 5013 Miller Trunk Highway, Duluth, MN). As well as being located in a larger metropolitan area (Duluth’s population is just over 86,000 residents), the site was also conveniently located for the NRRI PM Study Team. Because this site was located on the north end of town, it is removed from the influence of other industries within the city of Duluth as well as potential inversion effects created by the adjacent topographic highs and Lake Superior bay.
Minneapolis – University of Minnesota Mechanical Engineering Building A third background site was selected late in the sampling campaign of this study and is located approximately 200 miles south of the primary study area. This site was deemed critical in order to evaluate ambient PM levels in a metropolitan center far removed from the taconite industry of northeastern Minnesota. To the NRRI researchers and their collaborators, it seemed prudent that size- fractionated aerosol PM samples should also be collected and included in this study from the largest metropolitan area in Minnesota for comparative purposes. Since the NRRI particle study team was already collaborating closely with airborne particle scientists at the University of Minnesota’s Minneapolis campus, a logical choice for the metropolitan sampling locations was atop the five-story rooftop of the Mechanical Engineering Building at the University of Minnesota Twin Cities (NAD 83 UTM North 481605 easting, 4980250 northing, elevation 1219’). The site was centrally located on the University of Minnesota campus, which is located immediately east of downtown Minneapolis.
MIR Community Sampling Sites The sampling of MIR communities and background locations began in November 2008 and continued until June 2011. A total of 78 sample series were collected during this time period, including at least three sample series from both the winter season (November through April) and summer season (May through October) at each location. The five MIR locations selected were chosen with respect to location and population; community sample sites were not based on a grid system. Highest priority for selecting the sampling sites went to the most populous locations closest to taconite mines and/or processing facilities. The community sampling locations are (from west to east): 1) Keewatin; 2) Hibbing; 3) Virginia; 4) Babbitt; and 5) Silver Bay. Following is a brief geographic description of each of the locations. Two of the background sampling locations were chosen for their proximity to the study area, but without any influence from potential source PM, and include one site north (Ely) of and a second site south of (Duluth) the MIR. The third background site was chosen from a major metropolitan area (Minneapolis) for comparison purposes. Refer to Figure 2 to reference the sampling locations. Figure 4 shows the location of each Minnesota taconite mining operation and nearby communities.
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Figure 4. Map of Minnesota’s taconite mining operations. The dashed line demarcates western and eastern MIR taconite operations.
A more detailed description of each of the sites, including relationship to community boundaries, proximity to taconite operations (potential sources), and seasonal prevailing wind directions is addressed in greater detail in the Data Interpretation section of this report.
Keewatin Elementary School The town of Keewatin, MN is located on US Highway 169, on the western end of the MIR in Itasca County. The community has a population just over 1,000 residents. Keewatin was chosen as a sampling site because it is the closest town to the Keetac Taconite Plant (~1.5 miles northeast of town) and is approximately 20 miles northeast of the furthest western extremities of the MIR. The community sample site at Keewatin Elementary School (NAD 83 UTM North 493963 easting, 5249647 northing, elevation 1537’) is located at the intersection of South 3rd Street and West 4th Avenue, which is centrally positioned on the north end of the town of Keewatin. The sampling equipment was located on the northern edge of the three-story rooftop, near the roof access and away from any structures that would adversely affect meteorological conditions.
Hibbing High School Approximately 10 miles to the east of Keewatin, MN is Hibbing, MN, the location of another NRRI community sampling site. The city of Hibbing is centered between the towns of Keewatin and Chisholm and has just over 16,000 full-time residents. It is also the closest population center to the Hibtac Taconite Plant (~4 miles northwest of town). The Hibbing sampling site was located on the roof of the historic Hibbing High School (NAD 83 UTM North 505069 easting, 5252477 northing, elevation 1557’), which is located between East 21st and 23rd Streets, and also between 7th and 9th Avenues East. The sample equipment was located on the northern edge of the west wing of the four-story rooftop, away from any obstructions that might have influenced data collection.
Virginia City Hall Further east (roughly 25 miles from Hibbing), where US Highways 169 and 53 intersect, is the city of Virginia, MN. Virginia has a population of nearly 8,000 residents and is centrally located within the MIR and St. Louis County. The city of Virginia is situated in a basin (topographic low) just south of the Laurentian Divide and is nearly surrounded by iron mining activity. Virginia was chosen as a sampling site
NRRI/RI-2019/30 – Community Gravimetric Analysis 21 because of its unique central placement between three operating taconite facilities: the Minntac Taconite Plant (~5 miles northwest of town), the Minorca Taconite Plant (~3 miles northeast of town), and the Utac Thunderbird Taconite Mine (~2 miles south of town). The community sample site was located on the rooftop of the Virginia City Hall (NAD 83 UTM North 534894 easting, 5263337 northing, elevation 1593’) that is located at the intersection of South 4th Avenue West and 1st Street South, close to the city center.
Babbitt Municipal Building From Virginia, MN, approximately 40 miles northeast along County Highway 21 (paralleling the MIR) is the town of Babbitt, MN. Babbitt is located on the eastern border of St. Louis County and has a population of roughly 1,500 residents. It is the closest population center to Cleveland-Cliffs Inc.’s Peter Mitchell Taconite Mine and primary crusher (~3.5 miles southeast of town). The community sample site was located on the rooftop of the Babbitt Municipal Building (NAD 83 UTM North 579583 easting, 5284327 northing, elevation 1518’), which is situated on the south end of town on South Drive.
Silver Bay High School The geographical feature designated as the MIR and its predominant rock constituent, the BIF, end approximately five miles northeast of the town of Babbitt, MN. With the exception of its primary crusher, Northshore Mining Company’s taconite processing plant is located roughly 45 miles to the southeast on the shores of Lake Superior in the town of Silver Bay. Silver Bay is located on Minnesota Highway 61 in Lake County and has a population of just over 1,800 residents. It was chosen as a sampling site because it is the closest population center to the Northshore Taconite Plant (~1 mile southeast of town). The rooftop community sample site was located at the Silver Bay (Kelley) High School (NAD 83 UTM North 630381 easting, 5239000 northing, elevation 926’), in the center of town between Banks Boulevard and Lake County Highway 15.
PARTICULATE MATTER SAMPLING In order to spatially, gravimetrically, mineralogically, and chemically characterize PM, the NRRI used three MSP second-generation micro-orifice uniform deposit impactors (120 MOUDI II) for the collection of size-fractionated PM (see http://www.mspcorp.com/ for more details). The equipment and methods used by the NRRI to characterize PM in the taconite plants were consistent throughout the sampling collection period. Performance and precision of the MOUDI instruments were tested in a USEPA-approved aerosol test chamber and shown to be consistent (Marple et al., 2014; Monson Geerts et al., 2019b). Application of the MOUDIs for long-term ambient sampling was also demonstrated by comparing size distributions (average PM2.5 and PM10) from the three background sites, which compare well with three-year averages over the same period conducted by state regulatory sampling (MPCA, 2013).
120 MOUDI II Cascade Impactor The three (3) 10-stage MOUDI II – model 120 cascade impactors utilized in this study are equipped with internal stepper-motor stage rotation to provide uniform particle deposition on collection substrates. These samplers are designed for precision, high-accuracy sampling (based on a flow rate of 30 L/min.) within a PM cut-size range from 18 µm to 0.056 µm (Photo 1). This size-fractionating of the aerosol particles allows for the designation of the PM into specific size classifications including: PM1, PM2.5, and PM10, which is part of the characterization as well as important for assessing mass weight. Table 10 indicates the MOUDI stages and size ranges based on aerodynamic diameter and log mean diameter. Based on the distribution of PM of various aerodynamic diameters collected by the MOUDI sampler, PM size fractions can be subdivided into which area of the human respiratory system they would affect (refer to right side of Table 10; Marple, 2010, pers. comm.).
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Photo 1. 120 MOUDI II cascade impactor.
A number of particle collection experiments using the MOUDI were conducted prior to the formal sampling program (Monson Geerts et al., 2019a). These experiments were completed to determine an adequate run time to collect a sufficient weight of PM for gravimetric, chemical, mineralogical, and morphological characterization. Because of the relatively low concentrations of mineral PM in northern Minnesota air, it was determined that the optimal particle sample run times for community locations be between 120 and 168 hours (5–7 days; Monson Geerts et al., 2019b). These sample times were also favorable for depositing sufficient PM (but not too much) that could easily be analyzed using a scanning electron microscope (SEM). Both the MOUDI and the Total Filter Sampler (TFS) were set up to collect samples at each community location. Sample collection may be set on the MOUDI sampler using a manual or timed start. For more details on sampling protocols, see Monson Geerts et al. (2019b).
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Table 10. MOUDI cascade impactor stages, ranges, and PM designations (Monson Geerts et al., 2019a).
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Respirable Weight Fraction PM2.5 The MOUDI cascade impactor fractionation is based primarily on the PM10 and PM1 cut sizes; therefore, it does not have a specific cut-size of PM2.5. However, a simple formula can be used to calculate the PM2.5 fraction from the ranges of particle sizes that are collected (B. Olson, 2011, pers. comm.), as follows:
PM2.5 = (SUM of MOUDI Stages 5-F) + MOUDI Stage 4 x [(LOG (2.5 ÷ 1.78)) ÷ (LOG (3.16 ÷ 1.78))]
[All MOUDI stage measurements in concentrations (µg/m3)]
where F = after filter stage
The PM2.5 fraction represents all of the PM with an aerodynamic size less than 2.5 µm. This would essentially include all of the particles impacted on MOUDI stage 5 and below and also include some of the particles on stage 4 (Table 8). This size fraction is commonly known as the “respirable fraction,” including PM small enough to affect tracheal, bronchial, bronchiolar, and alveolar regions of the human body (USEPA, 1997).
Total Filter Sampler (TFS) The MOUDI cascade impactor was accompanied at each sample location by a TFS. Filter substrates from the TFS are utilized for mineralogical and chemical analysis. The TFS sampler is simply designed, with no moving parts or electrical components (Photo 2). A mixed cellulose ester (MCE) filter substrate is placed in the holder of the TFS apparatus by screwing the two halves of the TFS filter holder together. The smaller-diameter outlet tube of the sampler is connected to a rotameter, which is then attached to the vacuum pump. The rotameter is utilized to adjust the pump volume to the desired vacuum, e.g., to establish a flow rate of 8 L/min. The setup procedures of both samplers are described in greater detail in Monson Geerts et al. (2019b).
Photo 2. Total Filter Sampler (TFS).
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Substrates and Gravimetric Analysis All substrates including polycarbonate, Teflon®, and MCE filters were conditioned prior to initial weighing and sampling. To drive off any volatiles, the polycarbonate and Teflon® substrates were conditioned in the oven at 125° C for one hour. Upon exiting the oven, each substrate was placed in its own petri slide, covered, and labeled with a series number. The impactor substrates were also stored in the desiccator for a minimum of 12 hours before weighing, both pre- and post-sampling. Following the desiccation period, the substrates were removed from the desiccator, covered, and immediately weighed. Due to their instability with regard to humidity (Bogen et al., 2011), the variance of the weights of MCE filters was found to be too great for reproducibility, and therefore, measurements of the MCE filter weights were completed for in-house comparisons to the total MOUDI weights only. Once samples were collected and returned to the NRRI, substrates were conditioned with the same pre-sampling methods—with the exception of the oven baking—to remove volatiles. Gravimetric analysis was performed in a dedicated aerosol particle laboratory at the NRRI within 24–48 hours of collection. All scales, balances, and biosafety cabinets were certified and calibrated annually. A Cahn 25 Automatic Electrobalance was used to weigh all substrates in micrograms (µg). All filters were non- consecutively weighed twice. If the weight difference was > 0.010 µg, the substrate was re-weighed two more times. Before, during, and after the weighing process, tare weights were also measured and recorded to keep record of any balance drift. Field blanks for each substrate type, as well as laboratory blanks, were also weighed. The field blanks were exposed to the environment during the collection period and underwent the same conditioning/transportation as the collection substrates. Following gravimetric analysis, the filter substrates were stored in their labeled dedicated plastic petri dishes in the original boxes in a clean, dry storage cabinet in the laboratory. They were stored there until they were needed for chemical and mineralogical analysis. For extended detail on pre-sampling, sampling techniques, and post-sampling procedures, see Monson Geerts et al. (2019b, specifically Appendix A).
Sampling Protocol Aluminum cabinets were specially designed and built to house the MOUDI and TFS collection equipment (Photo 3). The housing was secured to a wooden platform and stabilized with sand tubes and/or concrete blocks. Vacuum pump(s) were placed outside of the housing in a weatherproof plastic tote with silicon tubing running from the pump through the housing wall to the instrument. An omni- directional inlet was secured to the top of the housing by a PVC pipe, which allowed air to be collected from all directions. A Davis weather station (Vantage Pro2 w/ Integrated Sensor Suite) was mounted to the top of the inlet and recorded atmospheric data including wind speed and direction, temperature, and precipitation.
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Davis weather station
Omni-directional outlet
Aluminum equipment housing
Pump
Photo 3. Equipment housing with pump tote, omni-direction inlet, and Davis weather station located on the Babbitt Municipal Building rooftop.
At each of the community site locations, consideration was taken to locate the sample housing in an area of the roof that was least likely to be influenced by other structures, turbulent air flow patterns, or disruptions from non-related activities. The housings were undisturbed and remained in the same locations throughout the duration of the project. Sampling instruments inside the housing included both the MOUDI and the TFS, which sampled air collected through an omni-directional inlet directly below the Davis weather instrument. The inlet was connected to a 1½” PVC riser pipe, which passed through the roof of the housing and was connected to a PVC wye. Sample air was split between the MOUDI, and the TFS sampler was connected to the wye using braided conductive silicon tubing. A length of braided conductive silicon tube (1 cm inside diameter, or ID) was connected to the back of the MOUDI and then to a coupling located on the wall of the sampler housing. Similar tubing then was connected to a Swagelok regulating valve on the vacuum pump. Vacuum flow pressure was adjusted to 30 L/min. using the valve, and flow was measured through a TSI 4043 Mass Flowmeter. Similarly, the other end of the TFS was connected to a rotameter and then routed to either of two configurations: 1) directly to a separate TFS vacuum pump; or 2) to a splitter that splits the vacuum pressure with the MOUDI (Photo 4). All connections were made with the same smaller-diameter braided conductive silicon tubing. The TFS vacuum flow pressure was adjusted to 8 L/min. using a valve on the King 7530 2C-11 Rotameter and the TSI Mass Flowmeter. Rotameters were calibrated in the lab using the TSI mass flow meter.
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PVC wye air intake
Tubing
TFS sampler PVC wye air intake
Rotameter Light bulb
Photo 4. Internal setup of MOUDI cascade impactor and TFS sampler. The light bulb(s) is used for heating inside the sampling housing during winter conditions.
Cold Weather Sample Collection Temperatures on the MIR generally remain below freezing (0° C/32° F) throughout the duration of the winter. To protect the instrumentation during these cold conditions, the aluminum housings were insulated with ½” extruded polystyrene foam and heated with one or two light bulbs (Photo 4). Manufacturer information does not report the minimum temperature at which a MOUDI will continue to operate; however, sample collection at Keewatin Elementary School on January 27, 2009 (441 sample series) showed that the instruments continued to work in a heated and insulted housing at subzero temperatures. At the time of collection, the on-site weather station recorded a temperature of approximately -23° C (-9.4° F), while the MOUDI recorded an incoming air sample temperature of approximately 0° C (32° F), showing the effectiveness of an insulated and heated housing. The minimum ambient temperature during this run was -35° C (-31° F). Samples were also collected in an uninsulated housing at Hibbing High School on February 4, 2009 (451 sample series). The minimum ambient air temperature reached -32° C (-25.6° F), and there were no indications of collection problems associated with the cold temperature. Light bulbs remained on inside the housing throughout the collection period.
DATA REPORTING PROTOCOLS The gravimetric data that represent the aerosol PM sampling at the three background community sampling sites (Tables 11–13) and all five community locations (Tables 14–18) are listed below. All the gravimetric data are flow-weighted (concentration) with respect to the volume of air that was sampled during collection. Concentrations can then be compared for measurements from the same location as well as measurements between other locations. All gravimetric measurements that are part of this study are reported in weight/volume air (μg/m3) and/or as a mass (weight) percent (%) determined by size- fractionated data from the MOUDI II cascade impactors. (NOTE: The terms weight and mass are used interchangeably.) Tables 11–18 list all 78 sample series organized by MIR/background community location, sample date, season, and—where applicable—the activity of local mines/plant(s). Sample series from the tables include the measured PM concentrations and percentage of the total from each of the 10 MOUDI stages, in addition to the upper greased stage (30–18 µg/m3) and the after filter
NRRI/RI-2019/30 – Community Gravimetric Analysis 28
3 (≤ 0.056 µg/m ). Also included for each sample series is specific PM breakdown, including: PM1, PM2.5, and PM10. The specific PM fractions represent important PM designations defined as: . PM10 – coarse respirable particles that have aerodynamic diameters of 10 µm or less that can settle in the bronchi and lungs and cause health problems. . PM2.5 – fine respirable particles that have aerodynamic diameters of 2.5 µm or less that can settle in the gas exchange regions of the lungs (alveoli) and cause even more serious health problems. . PM1 – the point of aerodynamic diameter which divides the coarse and accumulation modes of particles and particles resulting from comminution versus combustion, respectively.
Compilation of the gravimetric data from all eight sampling locations by season is included in Table 19 (MOUDI totals) and Table 20 (MOUDI totals compared with PM2.5). Of the 78 total community samples collected, 36 were collected during the winter season (November–April) and 42 during the summer season (May–October). Similarly, the gravimetric data from the five MIR communities is summarized in Table 21 (MOUDI totals) and Table 22 (MOUDI totals compared with PM2.5) and organized by local mine/plant activity. Of the 54 total MIR community samples collected, 27 samples were collected during periods of where plants were inactive, and 27 samples were collected during periods when plants were active. A series of bar graphs were generated to assist in the visual comparison of PM concentrations from each of the MIR communities as well as the background sites. Figures 5 and 6 rank the MOUDI total and PM2.5 concentrations for all 78 samples collected from the eight community locations and indicate the season in which each of the samples were collected. Likewise, Figures 7 and 8 depict the average concentrations for both MOUDI total and PM2.5 for each location by season. Both sets of graphs (and accompanying summary tables) indicate slightly higher PM concentrations for samples collected during the winter season in the MIR communities. The background sites of Duluth and Minneapolis, however, show higher PM concentrations in the summer season. Both of these observations are supported by the statistical analyses of data, which is explained in greater detail below.
NRRI/RI-2019/30 – Community Gravimetric Analysis 29
Table 11. Ely Fernberg Site – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%).
Series 321 Series 341 Series 361 21-Nov-08 24-Nov-08 5-Dec-08 WINTER WINTER WINTER
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.85 10.4 0.81 5.7 0.21 3.2 1 18 to 10 0.56 6.9 0.89 6.3 0.23 3.4 2 10 to 5.62 0.97 11.9 0.82 5.8 0.28 4.1 3 5.62 to 3.16 0.83 10.1 0.95 6.7 0.28 4.1 4 3.16 to 1.78 0.49 6 0.65 4.6 0.15 2.3 5 1.78 to 1 0.42 5.2 1.4 9.9 0.31 4.5 6 1 to 0.562 0.84 10.3 2.1 14.8 0.4 5.9 7 0.562 to 0.316 1.3 15.9 2.12 14.9 0.8 11.8 8 0.316 to 0.178 0.72 8.8 0.73 5.2 0.45 6.6 9 0.178 to 0.1 0.46 5.7 0.9 6.3 0.46 6.9 10 0.1 to 0.056 0.42 5.1 0.77 5.4 0.31 4.6 F Less than 0.056 0.32 4 2.08 14.6 2.88 42.6
PM1 4.06 49.7 8.7 61.1 5.3 78.4
PM2.5 4.77 58.4 10.49 73.7 5.7 84.3
PM10 6.77 82.8 12.53 88 6.32 93.4 TOTAL 8.18 100 14.23 100 6.76 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 30
Table 11 (continued).
Series 1171 Series 1311 Series 2211 10-Aug-09 27-Oct-09 30-Sep-10 SUMMER SUMMER SUMMER
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.52 5.2 0.23 5.6 0.1 1.8 1 18 to 10 0.48 4.7 0.26 6.4 0.21 3.8 2 10 to 5.62 1.05 10.4 0.27 6.7 0.54 9.7 3 5.62 to 3.16 0.51 5 0.35 8.5 0.58 10.6 4 3.16 to 1.78 0.72 7.1 0.3 7.3 0.41 7.5 5 1.78 to 1 0.77 7.7 0.33 7.9 0.36 6.6 6 1 to 0.562 1.02 10.1 0.38 9.4 0.46 8.4 7 0.562 to 0.316 1.21 12 0.58 14.1 0.62 11.2 8 0.316 to 0.178 1.15 11.4 0.33 7.9 0.49 8.9 9 0.178 to 0.1 0.71 7.1 0.3 7.3 0.42 7.6 10 0.1 to 0.056 0.67 6.6 0.27 6.5 0.39 7.1 F Less than 0.056 1.29 12.8 0.51 12.3 0.93 16.9
PM1 6.05 59.9 2.36 57.6 3.32 60.1
PM2.5 7.25 71.8 2.86 69.8 3.93 71.1
PM10 9.1 90.1 3.61 88 5.21 94.4 TOTAL 10.1 100 4.1 100 5.52 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 31
Table 12. Duluth – Natural Resources Research Institute – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%).
Series 301 Series 461 Series 491 Series 1331 17-Nov-08 4-Feb-09 2-Mar-09 28-Oct-09 WINTER WINTER WINTER SUMMER
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.8 11.8 0.3 3.7 0.49 6.1 0.2 3.9 1 18 to 10 0.42 6.3 0.48 5.9 0.57 7 0.3 6.1 2 10 to 5.62 0.54 8 0.43 5.4 0.57 7 0.33 6.7 3 5.62 to 3.16 0.26 3.8 0.5 6.2 0.52 6.4 0.36 7.3 4 3.16 to 1.78 0.31 4.6 0.54 6.7 0.69 8.5 0.29 5.8 5 1.78 to 1 0.42 6.2 0.54 6.6 0.79 9.8 0.27 5.4 6 1 to 0.562 0.66 9.7 0.98 12.2 0.77 9.5 0.61 12.3 7 0.562 to 0.316 1.65 24.3 0.77 9.6 0.85 10.4 0.69 13.9 8 0.316 to 0.178 0.46 6.7 0.85 10.5 0.64 7.9 0.72 14.5 9 0.178 to 0.1 0.45 6.7 0.48 5.9 0.61 7.6 0.35 7 10 0.1 to 0.056 0.43 6.3 0.79 9.8 0.53 6.5 0.34 6.8 F Less than 0.056 0.38 5.6 1.42 17.6 1.08 13.3 0.52 10.3
PM1 4.03 59.3 5.3 65.5 4.48 55.2 3.23 64.8
PM2.5 4.63 68.2 6.16 76.1 5.68 70 3.67 73.7
PM10 5.56 81.9 7.31 90.4 7.05 86.9 4.48 90 TOTAL 6.79 100 8.09 100 8.11 100 4.98 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 32
Table 12 (continued).
Series 2221 Series 2231 Series 2241 Series 2251 13-Oct-10 13-Oct-10 20-Oct-10 20-Oct-10 SUMMER SUMMER SUMMER SUMMER
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.99 8.5 0.95 8.2 1.14 12.4 1.78 9.1 1 18 to 10 1.44 12.4 2.8 24 1.25 13.6 2.43 12.4 2 10 to 5.62 1.47 12.7 1.54 13.2 1.23 13.4 2.1 10.7 3 5.62 to 3.16 1.32 11.4 1.17 10 1.12 12.2 2.12 10.8 4 3.16 to 1.78 1.16 10 0.75 6.4 0.85 9.2 1.53 7.8 5 1.78 to 1 0.82 7.1 0.43 3.7 0.55 5.9 1.2 6.1 6 1 to 0.562 0.65 5.6 0.43 3.7 0.43 4.7 0.48 2.4 7 0.562 to 0.316 0.85 7.3 0.76 6.5 0.76 8.3 1.18 6 8 0.316 to 0.178 0.69 5.9 0.67 5.8 0.51 5.5 3.36 17.1 9 0.178 to 0.1 0.67 5.8 0.57 4.9 0.43 4.7 2.08 10.6 10 0.1 to 0.056 0.45 3.9 0.35 3 0.25 2.7 0.74 3.8 F Less than 0.056 1.09 9.4 1.23 10.5 0.68 7.4 0.63 3.2
PM1 4.4 37.9 4.01 34.4 3.06 33.3 8.47 43.1
PM2.5 5.91 50.9 4.88 41.9 4.11 44.7 10.57 53.9
PM10 9.17 79 7.9 67.8 6.81 74 15.41 78.5 TOTAL 11.6 100 11.64 100 9.21 100 19.62 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 33
Table 12 (continued).
Series 2261 Series 2271 Series 2281 Series 2291 23-Nov-10 23-Nov-10 30-Nov-10 8-Dec-10 WINTER WINTER WINTER WINTER
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.07 2 0.25 3.7 0.24 3.8 0.08 2 1 18 to 10 0.07 1.9 0.35 5.2 0.3 4.6 0.15 3.6 2 10 to 5.62 0.14 3.6 0.5 7.4 0.33 5.1 0.17 4.2 3 5.62 to 3.16 0.14 3.8 0.49 7.2 0.34 5.2 0.19 4.8 4 3.16 to 1.78 0.08 2.1 0.57 8.4 0.28 4.3 0.19 4.8 5 1.78 to 1 0.21 5.4 0.49 7.2 0.32 5 0.25 6.3 6 1 to 0.562 1.01 26.5 0.91 13.4 1.5 23 0.75 18.6 7 0.562 to 0.316 1.21 31.9 1.1 16.3 1.74 26.7 1.29 31.9 8 0.316 to 0.178 0.27 7 0.76 11.1 0.53 8.2 0.34 8.3 9 0.178 to 0.1 0.07 2 0.55 8.1 0.29 4.5 0.17 4.1 10 0.1 to 0.056 0.02 0.4 0.34 5 0.22 3.4 0.14 3.4 F Less than 0.056 0.51 13.4 0.48 7 0.41 6.3 0.32 7.9
PM1 3.08 81.2 4.13 60.8 4.69 72.1 3.01 74.3
PM2.5 3.34 87.8 4.96 73 5.18 79.6 3.38 83.4
PM10 3.65 96.1 6.18 91.1 5.97 91.7 3.82 94.4 TOTAL 3.8 100 6.79 100 6.51 100 4.05 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 34
Table 13. Minneapolis – University of Minnesota, Mechanical Engineering Building – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%).
Series 2301 Series 2311 Series 2321 15-Feb-11 31-Mar-11 21-Apr-11 WINTER WINTER WINTER
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.85 5.6 1.07 8.1 2.24 20 1 18 to 10 1.2 7.8 1.63 12.3 0.98 8.8 2 10 to 5.62 1.13 7.4 1.1 8.3 0.75 6.7 3 5.62 to 3.16 0.97 6.3 0.84 6.3 0.74 6.6 4 3.16 to 1.78 0.82 5.4 0.86 6.5 0.78 6.9 5 1.78 to 1 0.75 4.9 0.69 5.2 0.66 5.9 6 1 to 0.562 2.19 14.3 1.32 9.9 0.74 6.6 7 0.562 to 0.316 2.04 13.3 1.59 12 1.04 9.3 8 0.316 to 0.178 3.5 22.9 1.78 13.4 1.11 9.9 9 0.178 to 0.1 0.69 4.5 1.01 7.6 0.64 5.7 10 0.1 to 0.056 0.41 2.7 0.61 4.6 0.56 5 F Less than 0.056 0.74 4.8 0.78 5.9 0.95 8.5
PM1 9.58 62.6 7.09 53.4 5.04 45
PM2.5 10.81 70.7 8.29 62.4 6.15 55
PM10 13.25 86.6 10.58 79.7 7.97 71.2 TOTAL 15.29 100 13.28 100 11.19 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 35
Table 13 (continued).
Series 2331 Series 2351 Series 2361 12-May-11 23-Jun-11 30-Jun-11 SUMMER SUMMER SUMMER
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 2.05 10.7 0.97 6.9 1.34 7.3 1 18 to 10 1.72 8.9 0.79 5.6 1.59 8.6 2 10 to 5.62 1.59 8.2 1.01 7.2 1.67 9.1 3 5.62 to 3.16 1.54 8 1.53 10.8 1.63 8.9 4 3.16 to 1.78 1.06 5.5 0.91 6.4 1 5.4 5 1.78 to 1 1.06 5.5 0.85 6 0.84 4.6 6 1 to 0.562 2.56 13.3 2.05 14.5 1.56 8.5 7 0.562 to 0.316 2.35 12.2 1.75 12.4 2.03 11 8 0.316 to 0.178 2.68 14 1.99 14.1 2.25 12.2 9 0.178 to 0.1 0.98 5.1 0.86 6.1 1.19 6.5 10 0.1 to 0.056 0.57 3 0.66 4.7 0.78 4.3 F Less than 0.056 1.06 5.5 0.74 5.2 2.51 13.7
PM1 10.21 53.1 8.06 57.1 10.33 56.2
PM2.5 11.9 61.9 9.45 66.9 11.76 63.9
PM10 15.46 80.4 12.36 87.6 15.47 84.1 TOTAL 19.23 100 14.11 100 18.4 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 36
Table 14. Keewatin Elementary School – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%).
Series 421 Series 441 Series 511 9-Jan-09 27-Jan-09 8-Mar-09 WINTER WINTER WINTER INACTIVE INACTIVE INACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.21 3.4 0.18 2.4 0.68 5 1 18 to 10 0.24 3.9 0.25 3.4 0.85 6.3 2 10 to 5.62 0.3 4.8 0.26 3.5 0.85 6.3 3 5.62 to 3.16 0.28 4.5 0.33 4.5 1.14 8.5 4 3.16 to 1.78 0.34 5.5 0.35 4.9 0.72 5.3 5 1.78 to 1 0.37 5.9 0.48 6.6 0.97 7.2 6 1 to 0.562 0.43 6.9 0.83 11.3 2.62 19.4 7 0.562 to 0.316 0.84 13.6 1.55 21.2 3.29 24.4 8 0.316 to 0.178 0.48 7.7 0.62 8.5 0.75 5.6 9 0.178 to 0.1 0.37 6 0.44 6 0.48 3.6 10 0.1 to 0.056 0.38 6.1 0.46 6.3 0.39 2.9 F Less than 0.056 1.97 31.7 1.56 21.3 0.75 5.6
PM1 4.46 72 5.46 74.6 8.27 61.3
PM2.5 5.03 81.2 6.16 84.1 9.67 71.7
PM10 5.75 92.7 6.89 94.1 11.96 88.7 TOTAL 6.2 100 7.32 100 13.49 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 37
Table 14 (continued).
Series 791 Series 981 Series 1011 Series 2201 16-Jun-09 27-Jul-09 2-Aug-09 30-Sep-10 SUMMER SUMMER SUMMER SUMMER INACTIVE INACTIVE INACTIVE ACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) mAir (µg/ 3) (%) mAir (µg/ 3) (%) mAir (µg/ 3) (%) mAir (µg/ 3) (%)
0 ≈30 to 18 0.77 6.2 0.5 5.2 0.48 6.2 0.32 4.9 1 18 to 10 0.78 6.3 0.54 5.6 0.61 7.8 0.5 7.6 2 10 to 5.62 0.79 6.3 0.67 7 0.68 8.8 0.65 9.9 3 5.62 to 3.16 0.87 7 0.95 9.9 0.85 10.9 0.61 9.4 4 3.16 to 1.78 0.68 5.5 0.65 6.7 0.51 6.6 0.51 7.7 5 1.78 to 1 0.71 5.7 0.63 6.5 0.54 6.9 0.4 6 6 1 to 0.562 0.66 5.3 1.19 12.3 0.69 8.8 0.5 7.6 7 0.562 to 0.316 1.67 13.4 1.15 11.9 0.69 8.8 0.85 13 8 0.316 to 0.178 1.65 13.2 0.91 9.5 0.6 7.7 0.52 8 9 0.178 to 0.1 1.18 9.4 0.57 5.9 0.45 5.8 0.38 5.8 10 0.1 to 0.056 0.87 7 0.57 6 0.44 5.7 0.34 5.2 F Less than 0.056 1.86 14.9 1.3 13.4 1.25 16 0.98 15
PM1 7.88 63.1 5.69 59 4.12 52.9 3.57 54.5
PM2.5 8.99 72 6.71 69.6 4.96 63.6 4.27 65.1
PM10 10.93 87.6 8.6 89.1 6.7 86 5.74 87.6 TOTAL 12.49 100 9.65 100 7.8 100 6.55 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 38
Table 15. Hibbing High School Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%).
Series 451 Series 521 Series 631 Series 681 4-Feb-09 8-Mar-09 13-Apr-09 27-Apr-09 WINTER WINTER WINTER WINTER ACTIVE ACTIVE ACTIVE ACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.5 6 1.26 8.3 0.81 7.3 1.13 9.7 1 18 to 10 0.74 8.8 1.46 9.6 1.11 10 1.24 10.6 2 10 to 5.62 0.71 8.6 1.27 8.3 1.03 9.4 1 8.5 3 5.62 to 3.16 0.74 8.9 1.77 11.6 0.9 8.2 0.92 7.9 4 3.16 to 1.78 0.64 7.7 0.53 3.5 0.69 6.3 0.52 4.4 5 1.78 to 1 0.73 8.8 0.84 5.5 0.6 5.4 0.96 8.2 6 1 to 0.562 1.12 13.4 2.27 14.9 0.89 8.1 0.85 7.3 7 0.562 to 0.316 1.1 13.3 2.51 16.5 1.41 12.8 1.13 9.7 8 0.316 to 0.178 0.54 6.5 2.04 13.4 1.34 12.1 0.66 5.7 9 0.178 to 0.1 0.41 4.9 0.41 2.7 0.79 7.2 0.61 5.2 10 0.1 to 0.056 0.31 3.7 0.26 1.7 0.74 6.7 0.63 5.4 F Less than 0.056 0.78 9.4 0.59 3.9 0.74 6.7 2.05 17.5
PM1 4.26 51.1 8.09 53.2 5.91 53.4 5.95 50.8
PM2.5 5.37 64.5 9.23 60.8 6.91 62.5 7.22 61.6
PM10 7.09 85.2 12.48 82.1 9.13 82.6 9.34 79.7 TOTAL 8.32 100 15.2 100 11.05 100 11.72 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 39
Table 15 (continued).
Series 711 Series 721 Series 781 Series 971 Series 1001 3-May-09 9-May-09 16-Jun-09 27-Jul-09 2-Aug-09 SUMMER SUMMER SUMMER SUMMER SUMMER ACTIVE ACTIVE INACTIVE INACTIVE INACTIVE
MOUDI MOUDI Stage Wt./Volume Wt./Volume Wt./Volume Wt./Volume Wt./Volume Percent (%) Percent (%) Percent (%) Percent (%) Percent (%) Stage # mRange (µ ) Airg (µ /m3) Airg (µ /m3) Airg (µ /m3) Airg (µ /m3) Airg (µ /m3)
0 ≈30 to 18 0.6 7.9 1.84 19.6 1.91 13.5 0.89 7.3 0.32 5.4 1 18 to 10 0.61 8.1 1.19 12.7 1.28 9.1 0.8 6.6 0.38 6.3 2 10 to 5.62 0.48 6.4 1.04 11.1 1.13 8 0.85 7 0.51 8.4 3 5.62 to 3.16 0.52 6.9 1.1 11.8 1.22 8.6 1.2 9.9 0.65 10.9 4 3.16 to 1.78 0.39 5.1 0.69 7.4 0.95 6.7 0.88 7.2 0.35 5.8 5 1.78 to 1 0.41 5.4 0.91 9.8 0.89 6.3 0.84 6.9 0.35 5.9 6 1 to 0.562 0.91 12 0.26 2.8 0.89 6.3 1.22 10.1 0.53 8.8 7 0.562 to 0.316 1.3 17.1 0.73 7.8 1.96 13.9 1.61 13.3 0.8 13.3 8 0.316 to 0.178 0.57 7.5 0.27 2.9 1.07 7.6 0.86 7.1 0.43 7.2 9 0.178 to 0.1 0.44 5.8 0.19 2 0.88 6.2 0.77 6.3 0.39 6.4 10 0.1 to 0.056 0.39 5.2 0.22 2.3 0.75 5.3 0.71 5.9 0.31 5.1 F Less than 0.056 0.95 12.6 0.91 9.7 1.21 8.6 1.5 12.3 0.99 16.5
PM1 4.56 60.2 2.58 27.6 6.76 47.8 6.68 55 3.44 57.3
PM2.5 5.2 68.7 3.9 41.7 8.21 58 8.04 66.2 4 66.6
PM10 6.36 84 6.33 67.6 10.95 77.4 10.45 86 5.3 88.3 TOTAL 7.57 100 9.35 100 14.15 100 12.14 100 6.01 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 40
Table 16. Virginia City Hall – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%).
Series 311 Series 471 Series 501 Series 571 Series 621 17-Nov-08 11-Feb-09 2-Mar-09 1-Apr-09 13-Apr-09 WINTER WINTER WINTER WINTER WINTER ACTIVE ACTIVE ACTIVE ACTIVE ACTIVE
MOUDI MOUDI Stage Wt./Volume Wt./Volume Wt./Volume Wt./Volume Wt./Volume Percent (%) Percent (%) Percent (%) Percent (%) Percent (%) Stage # Range (µm) Air (µg/m3) Air (µg/m3) Air (µg/m3) Air (µg/m3) Air (µg/m3)
0 ≈30 to 18 0.28 3.9 0.87 6.1 1.49 11 1.26 7.8 2.62 16.1 1 18 to 10 0.91 13 1.1 7.8 1.55 11.5 2.78 17.1 2.57 15.8 2 10 to 5.62 0.78 11.2 1.26 8.9 1.19 8.8 2.62 16.1 1.6 9.8 3 5.62 to 3.16 0.69 9.8 1.48 10.4 1.11 8.2 2.23 13.7 1.21 7.4 4 3.16 to 1.78 0.72 10.2 0.99 7 1.12 8.3 1.38 8.5 1 6.2 5 1.78 to 1 0.4 5.7 1.02 7.2 1.13 8.3 0.97 6 0.71 4.3 6 1 to 0.562 0.78 11.1 2.56 18 0.96 7.1 0.95 5.8 1.01 6.2 7 0.562 to 0.316 0.84 11.9 2.43 17.1 0.9 6.6 1.22 7.5 1.77 10.8 8 0.316 to 0.178 0.73 10.4 0.76 5.3 1.12 8.2 0.64 3.9 0.91 5.6 9 0.178 to 0.1 0.13 1.8 0.52 3.7 0.88 6.5 0.53 3.3 1.64 10.1 10 0.1 to 0.056 0.16 2.3 0.43 3 0.83 6.2 0.49 3 0.61 3.8 F Less than 0.056 0.6 8.6 0.78 5.5 1.25 9.3 1.18 7.3 0.63 3.9
PM1 3.24 46.2 7.48 52.6 5.94 43.9 5.01 30.9 6.58 40.4
PM2.5 4.06 57.9 9.08 63.9 7.73 57.1 6.79 41.8 7.88 48.4
PM10 5.83 83 12.23 86.1 10.48 77.5 12.2 75.1 11.1 68.1 TOTAL 7.02 100 14.21 100 13.53 100 16.24 100 16.3 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 41
Table 16 (continued).
Series 801 Series 811 Series 931 Series 961 Series 991 16-Jun-09 21-Jun-09 13-Jul-09 19-Jul-09 2-Aug-09 SUMMER SUMMER SUMMER SUMMER SUMMER INACTIVE INACTIVE INACTIVE INACTIVE ACTIVE
MOUDI MOUDI Stage Wt./Volume Wt./Volume Wt./Volume Wt./Volume Wt./Volume Percent (%) Percent (%) Percent (%) Percent (%) Percent (%) Stage # Range (µm) Air (µg/m3) Air (µg/m3) Air (µg/m3) Air (µg/m3) Air (µg/m3) 0 ≈30 to 18 1.09 8.3 1.43 8 0.85 7.9 2.61 24.7 0.69 9.5 1 18 to 10 1.3 9.9 1.51 8.4 1.37 12.7 0.71 6.7 0.69 9.5 2 10 to 5.62 1.17 8.9 1.65 9.2 0.98 9.1 0.83 7.8 0.75 10.2 3 5.62 to 3.16 1.19 9.1 1.57 8.7 1.04 9.7 0.85 8.1 0.76 10.5 4 3.16 to 1.78 0.93 7.1 1.45 8 0.8 7.4 0.61 5.7 0.58 8 5 1.78 to 1 0.76 5.8 0.71 3.9 0.65 6 0.58 5.5 0.4 5.6 6 1 to 0.562 0.91 6.9 1.62 9 0.74 6.9 0.78 7.4 0.58 7.9 7 0.562 to 0.316 1.47 11.2 2.81 15.6 0.9 8.3 0.81 7.7 0.73 10 8 0.316 to 0.178 0.99 7.5 1.3 7.2 0.92 8.6 0.81 7.7 0.56 7.7 9 0.178 to 0.1 0.88 6.7 0.96 5.3 0.62 5.7 0.56 5.3 0.41 5.7 10 0.1 to 0.056 0.77 5.9 0.77 4.3 0.63 5.8 0.57 5.4 0.38 5.2 F Less than 0.056 1.66 12.7 2.22 12.3 1.29 12 0.84 8 0.74 10.1
PM1 6.67 51 9.67 53.7 5.1 47.3 4.37 41.4 3.4 46.7
PM2.5 7.98 60.9 11.24 62.4 6.22 57.7 5.3 50.3 4.14 57
PM10 10.7 81.8 15.06 83.6 8.57 79.5 7.23 68.5 5.89 81 TOTAL 13.09 100 18.01 100 10.79 100 10.55 100 7.27 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 42
Table 17. Babbitt Municipal Building – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%).
Series 331 Series 351 Series 371 Series 531 21-Nov-08 24-Nov-08 5-Dec-08 17-Mar-09 WINTER WINTER WINTER WINTER ACTIVE ACTIVE ACTIVE ACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 1.57 7.6 0.71 5.3 0.55 8.2 0.48 4.2 1 18 to 10 2.08 10.1 0.79 6 0.65 9.8 0.57 5 2 10 to 5.62 1.8 8.7 0.93 7 0.51 7.6 0.59 5.2 3 5.62 to 3.16 1.14 5.5 0.87 6.6 0.22 3.3 0.83 7.3 4 3.16 to 1.78 0.87 4.2 0.8 6 0.36 5.3 0.8 7 5 1.78 to 1 0.89 4.3 0.8 6.1 0.32 4.8 0.89 7.9 6 1 to 0.562 0.99 4.8 2.86 21.6 0.55 8.2 1.88 16.5 7 0.562 to 0.316 1.56 7.6 2.18 16.5 0.9 13.4 2.55 22.4 8 0.316 to 0.178 1.6 7.7 0.88 6.7 0.65 9.7 0.93 8.2 9 0.178 to 0.1 1.17 5.7 0.64 4.9 0.53 7.9 0.57 5 10 0.1 to 0.056 1.38 6.7 0.69 5.2 0.41 6.1 0.43 3.8 F Less than 0.056 5.62 27.2 1.08 8.2 1.05 15.7 0.85 7.5
PM1 12.31 59.6 8.33 63 4.08 61 7.21 63.4
PM2.5 13.71 66.4 9.61 72.6 4.61 68.9 8.57 75.4
PM10 17.01 82.3 11.73 88.7 5.48 82 10.32 90.8 TOTAL 20.66 100 13.23 100 6.69 100 11.37 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 43
Table 17 (continued).
Series 551 Series 641 Series 671 Series 701 24-Mar-09 21-Apr-09 26-Apr-09 2-May-09 WINTER WINTER WINTER SUMMER ACTIVE INACTIVE INACTIVE INACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 1.16 11.8 1.18 10.6 1.64 15.2 0.66 9.6 1 18 to 10 0.63 6.4 0.98 8.8 1.05 9.7 0.74 10.7 2 10 to 5.62 0.47 4.8 0.91 8.1 0.73 6.8 0.72 10.4 3 5.62 to 3.16 0.53 5.4 1 8.9 0.72 6.6 0.77 11.2 4 3.16 to 1.78 0.56 5.7 0.76 6.8 0.62 5.8 0.74 10.7 5 1.78 to 1 0.73 7.5 0.72 6.4 0.49 4.5 0.85 12.3 6 1 to 0.562 1.38 14 1.1 9.8 0.87 8 0.58 8.4 7 0.562 to 0.316 1.58 16.1 1.47 13.2 1.26 11.7 1.01 14.6 8 0.316 to 0.178 0.66 6.7 0.84 7.5 0.65 6 0.16 2.3 9 0.178 to 0.1 0.53 5.4 0.73 6.5 0.58 5.3 0.09 1.4 10 0.1 to 0.056 0.52 5.3 0.67 6 0.58 5.4 0.04 0.6 F Less than 0.056 1.08 11 0.84 7.5 1.6 14.9 0.55 7.9
PM1 5.75 58.5 5.66 50.5 5.53 51.3 2.43 35.2
PM2.5 6.81 69.3 6.82 60.9 6.39 59.3 3.71 53.7
PM10 8.04 81.8 9.04 80.7 8.09 75.1 5.51 79.7 TOTAL 9.82 100 11.21 100 10.78 100 6.91 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 44
Table 17 (continued).
Series 741 Series 771 Series 831 Series 851 11-May-09 8-Jun-09 23-Jun-09 29-Jun-09 SUMMER SUMMER SUMMER SUMMER INACTIVE INACTIVE INACTIVE INACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 1.98 25.2 0.66 9.5 0.5 4 0.85 7.8 1 18 to 10 0.85 10.8 0.7 10 0.67 5.3 1.03 9.5 2 10 to 5.62 0.85 10.8 0.64 9.2 0.89 7.1 0.87 8 3 5.62 to 3.16 0.84 10.7 0.6 8.6 1.29 10.2 1.11 10.2 4 3.16 to 1.78 0.88 11.2 0.51 7.3 0.88 7 1.13 10.5 5 1.78 to 1 0.71 9 0.38 5.5 0.77 6.1 0.7 6.5 6 1 to 0.562 0.16 2.1 0.5 7.1 1.43 11.4 0.73 6.7 7 0.562 to 0.316 0.36 4.6 0.58 8.3 1.85 14.8 0.92 8.5 8 0.316 to 0.178 0.11 1.4 0.57 8.1 1.42 11.3 1.03 9.5 9 0.178 to 0.1 0.12 1.5 0.53 7.6 0.81 6.5 0.63 5.8 10 0.1 to 0.056 0.07 0.9 0.53 7.6 0.78 6.2 0.6 5.5 F Less than 0.056 0.93 11.9 0.78 11.2 1.26 10.1 1.24 11.4
PM1 1.75 22.3 3.48 49.9 7.56 60.2 5.15 47.5
PM2.5 2.97 37.9 4.17 59.7 8.86 70.5 6.52 60.2
PM10 5.02 64 5.62 80.5 11.39 90.7 8.96 82.7 TOTAL 7.84 100 6.99 100 12.56 100 10.83 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 45
Table 17 (continued).
Series 921 Series 951 Series 1161 Series 1301 13-Jul-09 19-Jul-09 10-Aug-09 25-Sep-09 SUMMER SUMMER SUMMER SUMMER ACTIVE ACTIVE ACTIVE ACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 1.3 13.3 0.47 5.9 0.54 5.3 0.5 5.1 1 18 to 10 1.19 12.2 0.54 6.9 0.64 6.3 0.57 5.9 2 10 to 5.62 0.71 7.3 0.65 8.2 0.75 7.4 1.04 10.7 3 5.62 to 3.16 0.85 8.7 0.81 10.2 0.98 9.6 1.41 14.5 4 3.16 to 1.78 0.67 6.8 0.71 9 0.77 7.6 0.76 7.8 5 1.78 to 1 0.52 5.3 0.57 7.2 0.76 7.4 0.43 4.4 6 1 to 0.562 0.68 7 0.66 8.4 0.95 9.3 0.65 6.7 7 0.562 to 0.316 0.97 9.9 0.89 11.3 1.34 13.2 0.81 8.3 8 0.316 to 0.178 0.62 6.4 0.78 9.9 0.79 7.7 1.39 14.3 9 0.178 to 0.1 0.52 5.3 0.64 8.1 0.6 5.9 0.67 6.8 10 0.1 to 0.056 0.41 4.2 0.53 6.7 0.62 6.1 0.54 5.5 F Less than 0.056 1.33 13.6 0.65 8.2 1.45 14.2 0.97 10
PM1 4.52 46.4 4.16 52.6 5.75 56.4 5.03 51.6
PM2.5 5.43 55.8 5.16 65.2 6.96 68.3 5.91 60.6
PM10 7.26 74.5 6.91 87.2 9.01 88.4 8.68 89 TOTAL 9.75 100 7.92 100 10.19 100 9.75 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 46
Table 18. Silver Bay High School – Particulate matter concentrations: MOUDI samples converted to weight/volume air (μg/m3) and mass percent (%).
Series 651 Series 661 Series 691 Series 731 21-Apr-09 26-Apr-09 2-May-09 11-May-09 WINTER WINTER SUMMER SUMMER INACTIVE INACTIVE INACTIVE INACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 4.84 30.6 0.95 9.7 0.61 12.2 1.14 14.9 1 18 to 10 1.03 6.5 0.88 9 0.23 4.6 1.82 23.8 2 10 to 5.62 1.05 6.6 0.68 7 0.23 4.6 0.87 11.4 3 5.62 to 3.16 0.95 6 0.72 7.4 0.41 8.2 0.88 11.4 4 3.16 to 1.78 0.76 4.8 0.59 6 0.2 4.1 0.81 10.6 5 1.78 to 1 0.71 4.5 0.48 4.9 0.38 7.5 0.85 11.1 6 1 to 0.562 1.02 6.5 0.68 7 0.84 16.7 0.18 2.3 7 0.562 to 0.316 1.55 9.8 1.07 10.9 0.96 19.1 0.37 4.8 8 0.316 to 0.178 1.05 6.6 1.02 10.5 0.59 11.8 0.21 2.8 9 0.178 to 0.1 0.82 5.2 0.68 7 0.21 4.3 0.06 0.8 10 0.1 to 0.056 0.85 5.3 1.24 12.7 0.36 7.1 0.05 0.7 F Less than 0.056 1.2 7.6 0.78 8 0 0 0.41 5.3
PM1 6.49 41 5.48 56 2.95 58.7 1.28 16.8
PM2.5 7.65 48.3 6.31 64.5 3.45 68.6 2.62 34.2
PM10 9.97 62.9 7.95 81.3 4.18 83.1 4.7 61.3 TOTAL 15.84 100 9.78 100 5.02 100 7.66 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 47
Table 18 (continued).
Series 751 Series 821 Series 841 Series 911 8-Jun-09 23-Jun-09 29-Jun-09 13-Jul-09 SUMMER SUMMER SUMMER SUMMER INACTIVE INACTIVE INACTIVE ACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.78 9.6 0.88 6.4 0.79 8.4 1.05 10.8 1 18 to 10 0.82 10.2 0.84 6.1 0.86 9.1 0.98 10.1 2 10 to 5.62 0.73 9 1.06 7.7 0.78 8.2 0.88 9.1 3 5.62 to 3.16 0.53 6.6 1.01 7.4 0.89 9.5 0.8 8.2 4 3.16 to 1.78 0.41 5.1 0.85 6.2 0.72 7.6 0.72 7.4 5 1.78 to 1 0.39 4.9 0.91 6.7 0.64 6.8 0.6 6.2 6 1 to 0.562 0.58 7.2 1.82 13.3 0.72 7.7 0.75 7.7 7 0.562 to 0.316 0.78 9.6 2.43 17.7 1.03 10.9 0.95 9.8 8 0.316 to 0.178 0.6 7.4 1.23 9 0.7 7.4 0.69 7.2 9 0.178 to 0.1 0.59 7.3 0.91 6.6 0.66 7 0.78 8 10 0.1 to 0.056 0.56 6.9 0.86 6.3 0.55 5.8 0.59 6.1 F Less than 0.056 1.31 16.2 0.92 6.7 1.09 11.5 0.91 9.4
PM1 4.42 54.7 8.17 59.5 4.75 50.3 4.67 48.2
PM2.5 5.06 62.6 9.58 69.8 5.82 61.7 5.7 58.8
PM10 6.48 80.2 12 87.4 7.78 82.5 7.67 79.1 TOTAL 8.08 100 13.73 100 9.43 100 9.69 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 48
Table 18 (continued).
Series 941 Series 1181 Series 1661 Series 1671 19-Jul-09 17-Aug-09 13-Apr-10 29-Apr-10 SUMMER SUMMER WINTER WINTER ACTIVE ACTIVE ACTIVE ACTIVE
MOUDI MOUDI Stage Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Wt./Volume Percent Stage # Range (µm) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) Air (µg/m3) (%) 0 ≈30 to 18 0.89 10.9 4.18 18.1 2.41 16.9 2.13 17.2 1 18 to 10 0.67 8.2 1.53 6.6 1.85 13 1.97 16 2 10 to 5.62 0.61 7.6 1.97 8.5 1.38 9.7 1.09 8.8 3 5.62 to 3.16 0.75 9.2 1.98 8.6 1.23 8.6 1.21 9.8 4 3.16 to 1.78 0.74 9.1 1.21 5.2 1.07 7.5 1.14 9.3 5 1.78 to 1 0.66 8.1 1.23 5.3 0.95 6.6 0.82 6.7 6 1 to 0.562 0.58 7.2 2.09 9.1 1.07 7.5 0.59 4.8 7 0.562 to 0.316 0.92 11.3 3.21 13.9 1.52 10.7 1.02 8.3 8 0.316 to 0.178 0.66 8.1 1.46 6.3 0.83 5.8 0.59 4.8 9 0.178 to 0.1 0.6 7.3 0.99 4.3 0.61 4.3 0.51 4.2 10 0.1 to 0.056 0.49 6.1 0.86 3.7 0.48 3.3 0.38 3.1 F Less than 0.056 0.56 6.9 2.36 10.2 0.87 6.1 0.86 7
PM1 3.81 46.9 10.96 47.5 5.37 37.7 3.97 32.2
PM2.5 4.9 60.4 12.9 56 6.95 48.8 5.47 44.7
PM10 6.57 80.9 17.34 75.3 9.99 70.1 8.24 66.8 TOTAL 8.12 100 23.05 100 14.25 100 12.34 100
NRRI/RI-2019/30 – Community Gravimetric Analysis 49
Table 19. Summary table of average PM concentrations from communities by seasonal MOUDI totals – weight/volume air (µg/m3). WINTER SEASON SUMMER SEASON ALL SAMPLES (N=36) (N=42) 1Average 1Average 1Average MOUDI Total MOUDI Total MOUDI Total 3 3 3 (µg/m ) n (µg/m ) n (µg/m )
Keewatin Elementary School, n=7 9.07 3 9.00 4 9.12
Hibbing High School, n=9 10.61 4 11.57 5 9.84
Virginia City Hall, n=10 12.70 5 13.46 5 11.94 Babbitt Municipal Building, n=16 10.41 7 11.97 9 9.19
Silver Bay High School, n=12 11.42 4 13.05 8 10.60
Ely Fernberg Site, n=6 8.15 3 9.73 3 6.57
Duluth – NRRI, n=12 8.43 7 6.31 5 11.41 Minneapolis - UMN Mech. Eng. Bldg., n=6 15.25 3 13.25 3 17.25
MIR COMMUNITIES 2 AVERAGE 10.92 12.02 10.09 2 MEDIAN 10.37 11.72 9.65 2 STANDARD DEVIATION 3.74 3.62 3.68
BACKGROUND 2 AVERAGE 10.07 8.70 11.68 2 MEDIAN 8.69 8.09 11.60 2 STANDARD DEVIATION 4.83 3.69 5.66
1Averages determined from all flow-weighted [weight/volume air 3 (µg/m )] raw data collected (see Tables 11–18). 2Statistical determinations from all flow-weighted [weight/volume air 3 (µg/m )] raw data collected (see Tables 11–18).
NRRI/RI-2019/30 – Community Gravimetric Analysis 50
3 Table 20. Summary table of average PM concentrations from communities by season, including: PM2.5 fraction – weight/volume air (µg/m ), and PM2.5 representative percent (%) of MOUDI total.
ALL SAMPLES WINTER SEASON (N=36) SUMMER SEASON (N=42) 1 1 1 1Average Average 1Average Average 1Average Average
MOUDI PM2.5 MOUDI PM2.5 MOUDI PM2.5 PM2.5 (%) n PM2.5 (%) n PM2.5 (%) Total Fraction Total Fraction Total Fraction 3 3 3 (µg/m ) (µg/m3) (µg/m ) (µg/m3) (µg/m ) (µg/m3)
Keewatin Elementary School 9.07 6.54 72.5 3 9 6.95 79 4 9.12 6.23 67.6 Hibbing High School 10.61 6.45 61.2 4 11.57 7.18 62.3 5 9.84 5.87 60.3 Virginia City Hall 12.7 7.04 55.7 5 13.46 7.11 53.8 5 11.94 6.98 57.7 Babbitt Municipal Building 10.41 6.64 62.8 7 11.97 8.08 67.6 9 9.19 5.52 59.1 Silver Bay High School 11.42 6.37 56.5 4 13.05 6.59 51.5 8 10.6 6.25 59 Ely Fernberg Site 8.15 5.83 71.5 3 9.73 6.99 72.1 3 6.57 4.68 70.9 Duluth - NRRI 8.43 5.21 66.9 7 6.31 4.76 76.9 5 11.41 5.83 53 MPLS - UMN Mech. Eng. Bldg. 15.25 9.73 63.5 3 13.25 8.42 62.7 3 17.25 11.04 64.3
MIR COMMUNITIES 2AVERAGE 10.92 6.61 61.1 12.02 7.31 62.4 10.09 6.09 60.1 2MEDIAN 10.37 6.35 61.6 11.72 6.91 62.5 9.65 5.43 60.9 2STANDARD DEVIATION 3.74 2.34 10 3.62 2.08 11.1 3.68 2.42 9.1
BACKGROUND 2AVERAGE 10.07 6.49 67.2 8.7 6.12 72.5 11.68 6.94 61 2MEDIAN 8.69 5.69 69.9 8.09 5.68 73 11.6 5.91 63.9 2STANDARD DEVIATION 4.83 2.87 11.9 3.69 2.38 10 5.66 3.42 11.3
1Averages determined from the flow-weighted [weight/volume air (µg/m3)] raw data. 2Statistical determinations from the flow-weighted [weight/volume air (µg/m3)] raw data.
NRRI/RI-2019/30 – Community Gravimetric Analysis 51
Table 21. Summary table of average PM concentrations from MIR communities by local mine/plant activity MOUDI totals - weight/volume air (µg/m3).
INACTIVE PLANT ACTIVE PLANT ALL SAMPLES (N=27) (N=27)
1Average MOUDI Total 1Average MOUDI Total 1Average MOUDI Total n n (µmg/ 3) (µmg/ 3) (µmg/ 3)
Keewatin Elementary School, n=7 9.07 6 9.49 1 6.55
Hibbing High School, n=9 10.61 3 10.76 6 10.54
Virginia City Hall, n=10 12.7 4 13.11 6 12.43
Babbitt Municipal Building, n=16 10.41 7 9.59 9 11.04
Silver Bay High School, n=12 11.42 7 9.94 5 13.49
2AVERAGE 10.92 10.31 11.52 2MEDIAN 10.37 10.55 10.19 2STANDARD DEVIATION 3.74 3.22 4.17
1Averages determined from the flow-weighted [weight/volume air (µg/m3)] raw data and by season. 2Statistical determinations from the flow-weighted [weight/volume air (µg/m3)] raw data and by season.
NRRI/RI-2019/30 – Community Gravimetric Analysis 52
Table 22. Summary table of average particulate matter concentrations from MIR communities by local mine/plant activity, including: PM2.5 3 fraction – weight/volume air (µg/m ), and PM2.5 representative percent (%) of MOUDI total.
ALL SAMPLES INACTIVE PLANT (N=27) ACTIVE PLANT (N=27)
1 1 1 1Average Average 1Average Average 1Average Average MOUDI PM2.5 MOUDI PM2.5 MOUDI PM2.5 PM2.5 (%) PM2.5 (%) PM2.5 (%) Total Fraction Total Fraction Total Fraction 3 3 3 (µg/m ) (µg/m3) (µg/m ) (µg/m3) (µg/m ) (µg/m3)
Keewatin Elementary School, n=7 9.07 6.54 72.5 9.49 6.92 73.7 6.55 4.27 65.1 Inactive (n=6), Active (n=1) Hibbing High School, n=9 10.61 6.45 61.2 10.76 6.75 63.6 10.54 6.31 60 Inactive (n=3), Active (n=6) Virginia City Hall, n=10 12.7 7.04 55.7 13.11 7.69 57.8 12.43 6.61 54.4 Inactive (n=4), Active (n=6) Babbitt Municipal Building, n=16 10.41 6.64 62.8 9.59 5.63 57.5 11.04 7.42 67 Inactive (n=7), Active (n=9) Silver Bay High School, n=12 11.42 6.37 56.5 9.94 5.78 58.5 13.49 7.18 53.6 Inactive (n=7), Active (n=5)
2AVERAGE 10.92 6.61 61.1 10.31 6.39 62.1 11.52 6.83 60.1 2MEDIAN 10.37 6.35 61.6 10.55 6.31 62.4 10.19 6.79 60.8 2STANDARD DEVIATION 3.74 2.34 10 3.22 2.21 11 4.17 2.48 8.9
1Averages determined from the flow-weighted [weight/volume air (µg/m3)] raw data. 2Statistical determinations from the flow-weighted [weight/volume air (µg/m3)] raw data.
NRRI/RI-2019/30 – Community Gravimetric Analysis 53
Comparison of All Community Samples by Season - MOUDI Totals [Weight / Volume Air (µg/m3)] 25
20 ) 3
15
10 Concentration - Weight / Volume Air (µg/m
5
0 Ely Winter 361 Ely Winter 321 Ely Winter 341 Ely Summer 1171 Duluth Winter 491 Ely Summer 2211 Ely Summer 1311 Duluth Winter 461 Duluth Winter 301 Babbitt Winter 371 Babbitt Winter 551 Babbitt Winter 331 Babbitt Winter 641 Babbitt Winter 351 Babbitt Winter 531 Babbitt Winter 671 MPLS Winter 2321 Virginia Winter 311 Hibbing Winter 451 Virginia Winter 501 Virginia Winter 571 Virginia Winter 471 MPLS Winter 2311 MPLS Winter 2301 Duluth Winter 2291 Hibbing Winter 521 Duluth Winter 2281 Virginia Winter 621 Hibbing Winter 681 Hibbing Winter 631 Duluth Winter 2271 Duluth Winter 2261 Babbitt Summer 951 Babbitt Summer 701 Keewatin Winter 421 Babbitt Summer 771 Babbitt Summer 921 Babbitt Summer 741 Keewatin Winter 441 Keewatin Winter 511 Babbitt Summer 851 MPLS Summer 2351 Babbitt Summer 831 MPLS Summer 2361 Virginia Summer 991 MPLS Summer 2331 Virginia Summer 961 Duluth Summer 2241 Hibbing Summer 721 Virginia Summer 811 Hibbing Summer 711 Hibbing Summer 971 Virginia Summer 801 Virginia Summer 931 Duluth Summer 1331 Duluth Summer 2251 Duluth Summer 2221 Hibbing Summer 781 Duluth Summer 2231 Babbitt Summer 1301 Silver Bay Winter 661 Babbitt Summer 1161 Silver Bay Winter 651 Hibbing Summer 1001 Keewatin Summer 981 Silver Bay Winter 1661 Silver Bay Winter 1671 Keewatin Summer 791 Silver Bay Summer 731 Silver Bay Summer 691 Silver Bay Summer 941 Silver Bay Summer 751 Silver Bay Summer 911 Silver Bay Summer 841 Silver Bay Summer 821 Keewatin Summer 1011 Keewatin Summer 2201 Silver Bay Summer 1181
Figure 5. Comparison of all community concentrations by season – MOUDI totals (weight/volume air – µg/m3).
NRRI/RI-2019/30 – Community Gravimetric Analysis 54
Comparison of All Community Samples by Season - PM2.5 Fraction [Weight / Volume Air (µg/m3)] 25
20 ) 3
15
10 Concentration - Weight / Volume Air (µg/m
5
0 Ely Winter 361 Ely Winter 321 Ely Winter 341 Ely Summer 1311 Duluth Winter 301 Duluth Winter 461 Ely Summer 2211 Duluth Winter 491 Ely Summer 1171 Babbitt Winter 371 Babbitt Winter 671 Babbitt Winter 551 Babbitt Winter 331 Babbitt Winter 531 Babbitt Winter 641 Babbitt Winter 351 Virginia Winter 311 MPLS Winter 2321 MPLS Winter 2301 Virginia Winter 571 Hibbing Winter 451 MPLS Winter 2311 Hibbing Winter 521 Hibbing Winter 681 Virginia Winter 621 Hibbing Winter 631 Duluth Winter 2281 Virginia Winter 471 Duluth Winter 2291 Virginia Winter 501 Duluth Winter 2271 Duluth Winter 2261 Babbitt Summer 701 Babbitt Summer 921 Babbitt Summer 771 Keewatin Winter 441 Keewatin Winter 421 Babbitt Summer 741 Babbitt Summer 951 Babbitt Summer 831 Babbitt Summer 851 Keewatin Winter 511 MPLS Summer 2331 MPLS Summer 2351 Duluth Summer 2221 MPLS Summer 2361 Hibbing Summer 711 Virginia Summer 961 Virginia Summer 931 Hibbing Summer 721 Virginia Summer 991 Duluth Summer 2241 Hibbing Summer 781 Duluth Summer 1331 Duluth Summer 2231 Virginia Summer 811 Virginia Summer 801 Hibbing Summer 971 Duluth Summer 2251 Babbitt Summer 1301 Silver Bay Winter 651 Babbitt Summer 1161 Silver Bay Winter 661 Hibbing Summer 1001 Silver Bay Winter 1671 Keewatin Summer 791 Silver Bay Winter 1661 Keewatin Summer 981 Silver Bay Summer 911 Silver Bay Summer 941 Silver Bay Summer 751 Silver Bay Summer 691 Silver Bay Summer 841 Silver Bay Summer 731 Silver Bay Summer 821 Keewatin Summer 1011 Keewatin Summer 2201 Silver Bay Summer 1181
3 Figure 6. Comparison of all community concentrations by season – PM2.5 (respirable) fraction of the MOUDI totals (weight/volume air – µg/m ).
NRRI/RI-2019/30 – Community Gravimetric Analysis 55
Figure 7. Comparison of community concentration averages by season and location – MOUDI totals [weight/volume air (µg/m3)].
NRRI/RI-2019/30 – Community Gravimetric Analysis 56
Comparison of Community Average Concentrations by Season / Location - PM2.5 [Weight / Volume Air (µg/m3)] 25
Virginia City Hall
20 ) 3
15
10 Concentrations - Weight / Volume Air (µg/m
5
0 Ely Winter, n=3 Ely Summer, n=3 Duluth Winter, n=7 MPLS Winter, n=3 Babbitt Winter, n=7 Virginia Winter, n=5 Hibbing Winter, n=4 MPLS Summer, n=3 Duluth Summer, n=5 Babbitt Summer, n=9 Keewatin Winter, n=3 Hibbing Summer, n=5 Virginia Summer, n=5 Silver Bay Winter, n=4 Keewatin Summer, n=4 Silver Bay Summer, n=8
3 Figure 8. Comparison of community concentration averages by season and location – PM2.5 fraction of MOUDI total [weight/volume air (µg/m )].
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TACONITE PARTICLE SOURCE INDEX To address the question “What is the source(s) of the particulate matter obtained during community sampling?”, an attempt was made to determine whether there was any correlation in the concentrations of PM (MOUDI total) and active/inactive iron mining/processing of taconite. It is important to note that determination of the potential correlation involves many variables. For example, stockpiles and tailings basins may produce PM even though the local mines and/or taconite processing plants are inactive. As well, other sources of mineral dust (e.g., unpaved roads, local rock and/or aggregate quarries, exposures of unconsolidated geological materials) may also contribute mineral PM to the atmosphere. Exact determinations of the source(s) of particulate matter sampled in this study were beyond the scope of this investigation. To broadly estimate the percentage of time during a community sampling event that PM could be derived from local mining/taconite processing operations, an index called the Taconite Particle Source Index (TPSI) was developed and subsequently calculated for each MIR community particulate matter sample collection series. The TPSI incorporates meteorological data collected at the time of sampling including wind speed, wind direction, the percentage of time that precipitation took place during an individual sampling series, and the amount of time that a sampling event occurred. The foundation of the TPSI is the Beaufort Wind Force Scale (https://www.rmets.org/resource/ beaufort-scale), which was developed in the early 1800s as an empirical measurement relating wind speed to observable conditions on land and sea. The Beaufort Index (see Table 23) indicates that weather vanes do not accurately determine the wind direction below a speed of 4 miles per hour (1.8 meters/second). Therefore, the TPSI is fundamentally based on the percent time that winds greater than 1.8 meters/second (4 mph) were blowing from a potential taconite processing plant/taconite mine and/or associated source area. Below this wind speed, weather vanes do not provide accurate wind vectors (WMO, 1970).
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Table 23. The Beaufort wind force scale (Royal Meteoroligical Society; https://www.rmets.org/resource/ beaufort-scale). Note that weather vanes do not give adequate wind vectors below 4 miles/hour (~1.8 meters/second). The TPSI developed in this report does not take into account winds less than 4 miles/ hour since wind directions cannot be determined using weather vanes such as that on the Davis Weather Station for winds below this speed.
Wind kilometers/ miles/ Description Knots Specifications Force hour hour 0 Calm <1 <1 <1 Smoke rises vertically 1 Light Air 1-5 1-3 1-3 Direction indicated by smoke drift but not wind vanes 2 Light Breeze 6-11 4-7 4-6 Wind felt on face; leaves rustle; wind vanes moved by wind 3 Gentle Breeze 12-19 8-12 7-10 Leaves and small twigs in constant motion; light flags extended 4 Moderate Breeze 20-28 13-18 11-16 Raises dust and loose paper; small branches moved 5 Fresh Breeze 29-38 19-24 17-21 Small trees in leaf begin to sway; crested wavelets form on inland waters 6 Strong Breeze 39-49 25-31 22-27 Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. 7 Near Gale 50-61 32-38 Whole trees in motion; inconvenience felt when walking against the wind 8 Gale 62-74 39-46 Twigs break off trees; generally impedes progress 9 Strong Gale 75-88 47-54 Slight structural damage (chimney pots and slates removed) 10 Storm 89-102 55-63 Seldom experienced inland; trees uprooted; considerable structural damage 11 Violent Storm 103-117 64-72 Very rarely experienced; accompanied by widespread damage 12 Hurricane 118+ 73+ Devastation
At each of the five community sample locations, an air photo was obtained and labeled with the potential sources along with the azimuth angles that include that source or sources from the sample collection site. Potential taconite mining/processing PM sources include the mines (including pits, haul roads, and active waste rock piles) as well as the local taconite processing facilities/plants and their associated tailings basins. The meteorological data that is collected by the Davis™ weather instruments or through the Weather Underground Stations (home website https://www.wunderground.com) during the actual time of sampling is used to calculate the TPSI. Davis™ instruments typically record conditions every hour, whereas Weather Underground stations record weather data approximately every 15 minutes. The percentage of time that PM could be derived from the plants and mines has been calculated based on the amount of time that the wind is blowing greater than 1.8 meters/second from these potential sources divided by the total sample duration. Precipitation was measured by the NRRI during the community sampling events described in this report. Precipitation values are measured by the Davis™ weather instrument in 0.25 mm increments.
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The precipitation values obtained from the Weather Underground Stations are measured and recorded in 0.01 inch increments, which is essentially the same as the Davis™ weather instrument. The NRRI generated the precipitation rose diagrams in millimeters/hour (see Discussion of Background and Community Sampling Results, this report). Because precipitation commonly causes airborne particulate matter to settle out of the atmosphere (Hinds, 1999), all wind measurements from potential sources at speeds over 1.8 meters/second, and that also contained any measurable amounts of precipitation, were subtracted to produce the TPSI. The Precipitation Correction Factor (PCF) subtraction was done to eliminate any potential bias produced by wind from a potential source that may actually have been suppressed due to precipitation in the atmosphere. The detailed equation (Eq. 2) for calculating TPSI is as follows:
TPSI (%) = [(Ts – Tcf) ÷ Tt] x 100 (Eq. 2)
Where: TPSI is the Taconite Particle Source Index, measured as a percentage; Tt is the total sample time; Ts is the amount of time that winds ≥ 1.8 m/s are blowing from a potential source (active/inactive) as defined above; and Tcf is the amount of time that Ts experienced measurable precipitation.
In the cases where multiple potential sources of PM from taconite processing plants and mine infrastructure exist, a more simplified version of Eq. 2 is used to derive the TPSI using the following equation:
TPSI (%) = (PLANT + MINE) – PCF (Eq. 3)
Where, TPSI is the Taconite Particle Source Index, measured as a percentage; PLANT is the percentage of time that winds with speeds ≥ 1.8 m/s were measured in directions from a potential plant or plant infrastructure source; MINE is the percentage of time that winds with speeds ≥ 1.8 m/s were measured in directions from a potential mine or mine infrastructure source; and PCF is a percentage time when precipitation was measured within vectors from a potential processing plant/mine and/or associated mining infrastructure source when wind speeds were ≥ 1.8 m/s.
Results of the community sampling campaigns conducted by the NRRI during this study for the three background sampling sites and the five MIR communities are discussed below. Included in these discussions are descriptions of the location of each of the sampling site, air photos indicating the locations of and vectors defining potential source directions from each of the taconite processing plant/mines and associated mining infrastructure relative to the sampling locations (MIR community sites only), information regarding weather conditions during sampling events (including rose diagrams containing wind and precipitation data), data pertaining to the amounts of PM sampled during the sampling events, and TPSI calculations by sample. Statistical information relating gravimetric results to the TPSI for each of the five MIR community sampling sites will be discussed in the Data Interpretation section of this report.
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DATA ANALYSIS
Statistical Analysis Statistical analyses were performed (using JMP Pro 11 (JMP, 2014) and R (R Core Team, 2014)) on the mean PM data from the three background sampling sites and five community sample locations. The statistical analysis was performed on average MOUDI totals, as well as the specific size fractions PM1, PM2.5, PM10, and Coarse PM (≥ PM2.5 ≤ PM10), and typically defines the amount of mineral PM or first mode of an aerosol sample (Hinds, 1999; USEPA, 1996). The PM measurements do not display normal distribution, so log10 transformation was applied to the raw data prior to statistical analysis. Correlation of MIR community PM concentrations and fractional percentages of total PM were analyzed inclusively compared with the Ely background site, as well as individually, for the variables of seasonal collection and local mine/plant activity. Results from T-tests for the overall (all community and background samples) comparison between winter and summer seasons indicate there is no significant seasonal difference for the fractional percent PM, but lower concentrations of MOUDI total, PM1, PM2.5 and PM10 in summer relative to winter are statistically significant (Table 24). However, when analyzed individually, there is no significant seasonal difference between winter and summer, except within the community location of Babbitt and the background site of Duluth (Table 25). In Babbitt, PM1 and PM2.5 concentrations and proportions tend to be larger in winter. In Duluth, the major seasonal difference is shown in the proportions of different particle sizes. In winter, there are more fine particles (PM10 and less) and less coarse particles than summer (Table 25). To address the question whether mining/taconite processing activities have an overall effect on the amount of PM in the MIR communities, community PM concentrations were compared with PM concentrations detected in the Ely background site. Overall comparisons of PM from MIR communities compared to PM from the Ely site are summarized in Table 26. A T-test with unequal variance was performed to examine if there was significant difference between the PM in MIR communities when local mines/plants were active and inactive versus PM concentrations in Ely. The p-values of the t-test are summarized in Table 27, and the results show there is no significant difference for any of the PM concentrations (either active or inactive local plants) between MIR communities and Ely but may have significant difference in PM size percentages. In Table 27, MIR+A is equivalent to all PM collected from the MIR communities during local active plants/mines, and MIR+I is the same, but during local inactive plants/mines. By percentage of the total PM, comparisons (PM1 through Coarse) between the MIR+A versus Ely were found to be significant; however, when plants were inactive, there were significant differences between the MIR sampling sites and Ely for PM2.5 and PM10 only. Each individual community was also evaluated separately to determine if PM concentrations were significant, comparing when the local mines/plants were inactive versus active (95% confidence level). Table 28 shows the results of the analysis between active and inactive local mines/plants for each of the five MIR communities. Note that the Keewatin community is not included in this analysis because it had only one sample collected during active mining/processing. All p-values were greater than 0.05, thus indicating no significant difference in PM concentrations or in fractional percentage between active and inactive conditions at any of the communities.
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Table 24. Results of T-tests comparing the average overall PM data for winter and summer concentrations for all MIR community samples.
% Log10 transformed N *TPSI PM1 PM2.5 PM10 Coarse MOUDI-T PM1 PM2.5 PM10 Coarse Summer 31 49.10 60.12 81.12 50.88 30.10 0.98 0.66 0.75 0.89 0.68 Mean Winter 23 52.38 62.35 80.76 47.63 32.96 1.06 0.77 0.85 0.96 0.73
Std Summer 31 10.85 9.15 7.49 10.85 15.00 0.14 0.20 0.17 0.15 0.15 Dev Winter 23 11.39 11.08 8.19 11.38 20.59 0.14 0.13 0.12 0.12 0.22 p-value 0.2913 0.4347 0.8686 0.2952 0.5759 0.0435 0.0169 0.0182 0.0415 0.3868 P-value less than 0.05 (bold, italics, and shadowed in yellow) indicates a significant seasonal difference. *TPSI/PM relationship is discussed in the TPSI section of this report.
Table 25. Mean and p-values from t-test to compare PM values between summer and winter.
% Log10
Community season PM1 PM2.5 PM10 Coarse MOUDI-T PM1 PM2.5 PM10 Coarse summer 46.89 59.09 81.88 53.08 0.96 0.61 0.72 0.87 0.67 Babbitt winter 58.19 67.54 83.04 41.82 1.06 0.82 0.88 0.97 0.67 p-value 0.024 0.050 0.743 0.024 0.143 0.032 0.049 0.151 0.966 summer 42.72 53.01 77.86 57.26 1.02 0.63 0.73 0.91 0.76 Duluth winter 66.92 76.89 90.34 33.06 0.78 0.61 0.67 0.74 0.29 p-value 0.009 0.009 0.022 0.009 0.074 0.750 0.496 0.138 0.023 summer 59.19 70.91 90.83 40.79 0.79 0.56 0.64 0.74 0.40 Ely winter 63.04 72.12 88.08 36.94 0.97 0.76 0.82 0.91 0.51 p-value 0.691 0.887 0.494 0.691 0.302 0.269 0.314 0.335 0.626 summer 49.58 60.25 80.68 50.39 0.97 0.65 0.75 0.88 0.66 Hibbing winter 52.16 62.34 82.39 47.87 1.05 0.77 0.85 0.97 0.73 p-value 0.685 0.699 0.679 0.691 0.379 0.273 0.271 0.295 0.540 summer 57.35 67.59 87.56 42.64 0.95 0.70 0.78 0.89 0.58 Keewatin winter 69.30 79.01 91.87 30.71 0.93 0.77 0.83 0.89 0.41 p-value 0.077 0.072 0.105 0.075 0.886 0.592 0.679 0.985 0.395 summer 55.45 64.25 84.01 44.57 1.23 0.98 1.04 1.16 0.88 Minneapolis winter 53.69 62.70 79.18 46.33 1.12 0.84 0.91 1.02 0.78 p-value 0.766 0.772 0.401 0.765 0.119 0.240 0.209 0.145 0.181 summer 47.83 59.01 78.74 52.15 0.98 0.64 0.75 0.88 0.69 Silver Bay winter 41.71 51.48 70.28 58.27 1.11 0.72 0.82 0.95 0.87 p-value 0.407 0.242 0.129 0.407 0.159 0.468 0.425 0.343 0.142 summer 48.02 57.63 78.86 52.00 1.06 0.74 0.82 0.95 0.77 Virginia winter 42.79 53.82 77.98 57.23 1.11 0.74 0.84 1.00 0.86 p-value 0.252 0.421 0.836 0.252 0.591 0.980 0.848 0.625 0.379 P-value less than 0.05 (bold, italics, and shadowed in yellow) indicate a significant seasonal difference.
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Table 26. Summary of mean and standard deviation for overall PM concentrations for MIR communities and Ely background.
% Log10 transformed N TPSI PM1 PM2.5 PM10 Coarse MOUDI-T PM1 PM2.5 PM10 Coarse MIR A* 27 49.50 60.06 80.62 50.50 32.93 1.04 0.72 0.81 0.94 0.73 Mean MIR I* 27 51.49 62.08 81.31 48.50 29.70 0.99 0.69 0.78 0.90 0.66
Ely 6 61.12 71.51 89.45 38.86 0.88 0.66 0.73 0.83 0.45 MIR A 27 9.53 8.94 6.82 9.52 17.09 0.15 0.16 0.14 0.14 0.18 Std Dev MIR I 27 12.57 10.99 8.64 12.57 18.03 0.14 0.20 0.16 0.14 0.18 Ely 6 9.42 8.29 4.21 9.45 0.19 0.20 0.20 0.19 0.23 *A represents active, I represents inactive.
Table 27. P-value of t-tests to compare overall PM means between MIR communities and the Ely background site.
% Log10 transformed TPSI PM1 PM2.5 PM10 Coarse MOUDI-T PM1 PM2.5 PM10 Coarse MIR+A vs. Ely 0.0278 0.0171 0.0016 0.0279 0.0987 0.4868 0.3722 0.2058 0.0309 MIR+I vs. Ely 0.0616 0.0414 0.0036 0.0620 0.2078 0.7619 0.5854 0.4047 0.0793 MIR+A vs. MIR+I 0.5171 0.4612 0.7437 0.5140 0.5033 0.2579 0.4750 0.4398 0.2822 0.1714 P-value less than 0.05 (bold, italics, and shadowed in yellow) indicates a significant difference.
Table 28. Mean and p-values from t-test between active and inactive conditions for MIR communities.
% Log10 MIR Parameters N TPSI PM1 PM2.5 PM10 Coarse MOUDI-T PM1 PM2.5 PM10 Coarse Active 9 56.94 66.94 84.98 43.05 21.89 1.02 0.77 0.85 0.95 0.65 Babbitt inactive 7 45.26 57.45 79.05 54.71 13.57 0.97 0.61 0.72 0.87 0.70 p-value 0.052 0.052 0.125 0.052 0.222 0.421 0.128 0.159 0.252 0.397 Active 6 49.41 59.95 80.21 50.60 37.67 1.01 0.69 0.78 0.91 0.71 Hibbing inactive 3 53.36 63.62 83.91 46.61 34.67 1.00 0.73 0.81 0.93 0.67 p-value 0.488 0.466 0.426 0.484 0.830 0.963 0.765 0.849 0.910 0.826 Active 5 42.50 53.64 74.43 57.48 34.00 1.10 0.72 0.83 0.97 0.86 Silver Bay inactive 7 48.14 58.54 76.98 51.84 27.71 0.97 0.62 0.73 0.85 0.67 p-value 0.414 0.414 0.603 0.415 0.476 0.227 0.459 0.364 0.252 0.135 Active 6 43.45 54.33 78.48 56.58 41.67 1.07 0.70 0.80 0.96 0.82 Virginia inactive 4 48.33 57.81 78.33 51.67 33.50 1.11 0.79 0.87 1.00 0.82 p-value 0.258 0.432 0.974 0.256 0.453 0.675 0.398 0.495 0.700 0.999
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PM/TPSI Statistical Analysis Statistical analyses were performed (using JMP Pro 11 (JMP, 2014) and R (R Core Team, 2014)) on the mean PM data from the five MIR community sample locations with respect to correlation with TPSI (95% confidence level). The correlation results (Table 29) show there is no overall significant correlation between PM and TPSI; in other words, no relationship was found between the PM concentrations or percent fractions of PM to that of prevailing winds from potential mining/processing sources. Again, there is no statistically significant seasonal difference between summer and winter TPSI values (see Table 24). Statistical evaluation of data from individual MIR communities comparing various size fractions of PM and TPSI shows that PM1, PM2.5, and PM10 have statistically significant correlation with TPSI in Babbitt and Virginia (Table 30). These results were irrespective of whether taconite processing plants/mines were active or inactive. Babbitt illustrates positive correlations between PM and TPSI, whereas Virginia illustrates negative correlations between PM and TPSI. The total PM (MOUDI) from Virginia also had negative significant correlation with TPSI.
Table 29. Overall MIR community Pearson correlations between PM variables and TPSI.
Correlation p-value PM1 % -0.2197 0.2709
PM2.5% -0.1819 0.3639
PM10 % -0.0492 0.8073 Coarse % 0.2205 0.269
log10 MOUDI-T -0.2598 0.1907
log10 PM1 -0.361 0.0643
log10 PM2.5 -0.3505 0.073
log10 PM10 -0.2912 0.1405
log10 Coarse -0.1129 0.5749
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Table 30. Individual MIR community Pearson correlation coefficients and p-values between other PM variables with TPSI.
Babbitt Hibbing Keewatin Silver Bay Virginia N 16 9 7 12 10
PM1 % 0.42 0.09 0.19 0.20 -0.18
PM2.5% 0.41 0.24 0.24 0.27 -0.19
PM10 % 0.42 0.33 0.39 0.41 -0.19 Coarse % -0.42 -0.09 -0.19 -0.20 0.18 Correlation log10 MOUDI-T 0.45 -0.56 -0.06 -0.27 -0.70 Coefficients log10 PM1 0.50 -0.43 0.01 -0.07 -0.73
log10 PM2.5 0.50 -0.45 0.01 -0.12 -0.76
log10 PM10 0.51 -0.50 -0.02 -0.15 -0.76
log10 Coarse 0.16 -0.50 -0.17 -0.31 -0.58
PM1 % 0.105 0.810 0.686 0.530 0.622
PM2.5% 0.114 0.536 0.599 0.396 0.591
PM10 % 0.105 0.387 0.386 0.187 0.607 Coarse % 0.105 0.813 0.684 0.528 0.618
p-value log10 MOUDI-T 0.080 0.116 0.890 0.404 0.023
log10 PM1 0.048 0.251 0.988 0.823 0.017
log10 PM2.5 0.046 0.228 0.978 0.700 0.010
log10 PM10 0.044 0.172 0.959 0.639 0.010
log10 Coarse 0.561 0.167 0.717 0.323 0.081 Significant difference (p < 0.05) is bold, italics, and shadowed in yellow.
DISCUSSION OF BACKGROUND AND COMMUNITY SAMPLING RESULTS
Background Locations
Ely Fernberg Site The geographical location (Fig. 2) and prevailing wind directions (Figs. 9a-b and 10a-b) made the Ely Fernberg site an ideal location for collecting background levels of PM. A total of six aerosol PM samples (three each for both winter and summer) were collected at Ely between November 2008 and September 2010.
Weather Conditions Wind direction and precipitation data obtained during sampling periods at the Ely Fernberg sampling site are illustrated in Figure 9a-b (winter season) and Figure 10a-b (summer season). For the winter season, winds were dominantly from the southwest to northwest directions, whereas in the summer season, winds were largely from the south, or from north-northwest to east directions (Figs. 9a, 10a). During the winter season, winds greater than 1.8 m/s (4 miles per hour) were blowing nearly 80% of the time; during summer, winds greater than 1.8 m/s were blowing approximately 59% of the time (Table 31). Measurable precipitation did not occur during the winter season sampling events; during the summer season, measurable precipitation occurred during 0.15% of the time that air sampling occurred (Figs. 9b, 10b).
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Figure 9a-b. Ely Fernberg Site winter season wind and precipitation composites.
Figure 10a-b. Ely Fernberg Site summer season wind and precipitation composites.
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Table 31. Weather conditions at the MIR communities and background sites. Percentages represent the amount of time that the winds at the sampling site were greater than 1.8 meters/second (4 feet/ second). The percentage = ((total amount of time - time < 1.8m/s)/total amount of time) x 100%. MIR Community Active % Inactive % Winter % Summer % Keewatin 80.2 56.5 65.9 58.5 Hibbing 74 53.7 75 62.4 Virginia 76.7 62.8 75 62.4 Babbitt 71.1 70.1 77.9 63.3 Silver Bay 59.1 61 66.3 59.8
Background Site Active % Inactive % Winter % Summer % Ely NA NA 79.5 58.5 Duluth NA NA 64.1 73.8 Minneapolis NA NA 37.9 38.3
Seasonal Comparison MOUDI totals ranged from a high of 14.23 µg/m3 in series 341 in winter to a low of 4.10 µg/m3 in series 1311 collected during the summer (Table 11). MOUDI total PM concentrations ranged from 6.76 µg/m3 to 14.23 µg/m3 in summer and 4.10 µg/m3 to 10.10 µg/m3 during the winter (Table 11). Figure 11a-b displays average size distribution plots (generated using DistFITTM2009.01; (Chimera Technologies, Inc., 1988–2012) of PM for winter (3 samples) and summer (3 samples) collected at the Ely Fernberg sampling site. Both graphs display faint bimodal distribution with slightly higher concentrations of PM in the “accumulation” mode (< PM1). Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the seasonal differences in PM of the Ely Fernberg background site showed no significant seasonal differences (Table 25). The average MOUDI total PM concentration for all samples collected at the Ely Fernberg site was 8.15 µg/m3 (Table 20). The seasonal average MOUDI totals varied considerably between winter season (9.73 µg/m3) and summer season (6.57 µg/m3). Of the eight community sites, the Ely Fernberg site had the lowest average MOUDI total PM concentrations for all samples collected (8.15 µg/m3; Tables 19 and 20). 3 The average PM2.5 concentration obtained from the Ely site for all samples was 5.83 µg/m , which is the second lowest recorded from the three background sites and the five MIR communities (Table 20). This value is lower than the average PM2.5 concentration for all samples obtained in the five MIR 3 3 communities (6.61 µg/m ) and the three background sampling sites (6.49 µg/m ). The average PM2.5 concentrations for samples collected at the Ely Fernberg site during winter and summer seasons were 3 3 6.99 µg/m and 4.68 µg/m . These values are lower than the average PM2.5 concentrations obtained during winter and summer sampling at the five MIR community sampling sites (7.31 µg/m3 and 3 6.09 µg/m , respectively). The Ely Fernberg average PM2.5 concentration during the winter season is greater than the average PM2.5 concentration for the winter season in the three background sites 3 (6.12 µg/m ) and lower than the average PM2.5 concentration identified in the three background sites for samples obtained during the summer season (6.94 µg/m3; Table 20).
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(a)
(b)
Figure 11a-b. Comparison of averaged MOUDI stages from Ely Fernberg Background Site by winter season (3 samples) and summer season (3 samples). Bars = St. Dev.
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The Ely site had the second-highest average percent PM2.5 fraction for all samples at 71.5%, considerably higher than the overall average percent PM2.5 fraction for all samples collected in the MIR communities (61.1%; Table 20), and higher than the average percent PM2.5 fraction obtained for all samples in the three background sampling sites (67.2%; Table 20). The higher average percentage of PM2.5 fraction may be due to the isolation of the Ely Fernberg site relative to industrial aerosol inputs in cities, as well as a lack of local sources of mineral dust generated from traffic on dirt roads in communities. At the Ely Fernberg site, the average PM2.5 concentrations were higher in the winter 3 3 (6.99 µg/m ) than summer (4.68 µg/m ; Table 20). These values compare with average PM2.5 concentration for winter sampling in the five MIR communities (7.31 µg/m3) and the three background 3 sites (6.12 µg/m ) as well as average summer PM2.5 concentration for summer sampling in the five MIR 3 3 communities (6.09 µg/m ) and the three background sites (6.94µg/m ). The average percent PM2.5 fraction at the Ely background site was higher (72.1%) during winter than during summer (70.9%; Table 20). These compare with the average percent PM2.5 for winter sampling in the five MIR communities (62.4%) and the three background sites (72.5%) as well as average percent PM2.5 during summer sampling in the five MIR communities (60.1%) and the three background sites (61.0%).
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Duluth – NRRI A total of 12 PM samples were collected at the Duluth background sampling site (located on the rooftop of the Natural Resources Research Institute) between November 2008 and December 2010 (Fig. 2). Seven sampling events took place during the winter season and five sampling events took place during the summer season.
Weather Conditions Wind direction and precipitation data obtained during sampling periods at the Duluth sampling site are illustrated in Figure 12a-b (winter season) and Figure 13a-b (summer season). For the winter season, winds were dominantly from the west-northwest directions, whereas in the summer season, winds were generally from the west (Figs. 12a, 13a). During the winter season, winds greater than 1.8 m/s (4 miles per hour) were blowing approximately 64% of the time; during summer, winds greater than 1.8 m/s were blowing nearly 74% of the time (Table 31). Measurable precipitation did not occur during the winter season sampling events; during the summer season, measurable precipitation occurred during approximately 1% of the time that air sampling occurred (Figs. 12b, 13b).
Seasonal Comparisons The MOUDI total PM concentrations ranged from 19.62 µg/m3 in series 2251 during the summer to 3.80 µg/m3 in series 2261 during the winter (Table 12). MOUDI total PM concentrations ranged from 4.98 µg/m3 to 19.62 µg/m3 in summer and 3.80 µg/m3 to 8.11 µg/m3 during the winter (Table 12).The MOUDI total from sample series 2261 (3.8 µg/m3) was the lowest recorded PM sample collected during this study. Figure 14a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for winter (7 samples) and summer (5 samples) collected at the Duluth NRRI sampling site. Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the seasonal differences in PM did show significant seasonal differences from the Duluth site (Table 25). In Duluth, the major seasonal difference is shown in the proportions of different particle sizes. In winter, there are more fine particles (< PM1) and less coarse particles than in summer season sampling. These significant differences are depicted by the graphs in Figure 14a-b. A faint bimodal distribution curve exists for PM concentrations from the winter season (Fig. 14a) dominated by a higher amount of finer particles ranging in size from 1.0 µm to less than 0.056 µm. These “accumulation” mode particles are typically composed of particles generated through chemical reactions, such as combustion (Hinds, 1999). This differs significantly compared with the summer season mean concentrations of PM from the Duluth site (Fig. 14b), where in this case, a distinct bimodal distribution of PM is displayed, with a typical higher concentration of “coarse” mode than “accumulation” mode. The average MOUDI total PM concentration for all samples collected at the Duluth background site was 8.43 µg/m3 (Table 20). The average MOUDI total PM concentration for all samples obtained during winter sampling in Duluth was 6.31 µg/m3, and the average MOUDI total PM concentration for all samples obtained during summer sampling at the Duluth background site was 11.41 µg/m3. These values compare with average MOUDI total PM concentrations for all samples collected during the winter season at the five MIR communities (12.02 µg/m3) and the three background sites (8.7 µg/m3) as well as the average MOUDI total PM concentrations for all samples collected during the summer season at the five MIR communities (10.09 µg/m3) and the three background sites (11.68 µg/m3).
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Figure 12a-b. Duluth – Natural Resources Research Institute winter season wind and precipitation composites.
Figure 13a-b. Duluth – Natural Resources Research Institute summer season wind and precipitation composites.
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(a)
(b)
Figure 14a-b. Comparison of averaged MOUDI stages from Duluth - NRRI Background Site by winter season (7 samples) and summer season (5 samples). Bars = St. Dev.
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The average PM2.5 fraction of the MOUDI totals for all samples collected at the Duluth background 3 site was 5.21 µg/m . This compares with the average PM2.5 fraction of the MOUDI totals for samples obtained from the five MIR communities (6.61 µg/m3) and the three background sampling sites 3 (6.49 µg/m ). The average PM2.5 fraction of MOUDI totals by season at the Duluth sampling site were 3 3 4.76 µg/m (winter) and 5.83 µg/m (summer; Table 20). This compares with the average PM2.5 fraction of the MOUDI totals obtained during the winter at the five MIR communities (7.31 µg/m3) and the three 3 background sampling sites (6.12 µg/m ), and the average PM2.5 fraction of the MOUDI totals obtained during the summer at the five MIR communities (6.09 µg/m3) and the three background sampling sites (6.94 µg/m3). The average percent PM2.5 fraction obtained for all samples collected at the Duluth background sampling site was 66.9%. This compares with the average PM2.5 fraction obtained for all samples from the five MIR communities (61.1%) and the three background communities (67.2%; Table 20). The average percent PM2.5 fraction obtained for samples collected at the Duluth background sampling site during the winter season was 76.9%. This compares with the average PM2.5 fraction obtained for samples collected during the winter season from the five MIR communities (62.4%) and the three background communities (72.5%; Table 20). The average percent PM2.5 fraction obtained for samples collected at the Duluth background sampling site during the summer season was 53.0%. This compares with the average PM2.5 fraction obtained for samples collected during the summer season from the five MIR communities (60.1%) and the three background communities (61.0%; Table 20). It is currently unclear why these differences occur between the seasonal sampling in Duluth; they may be related to prevailing winds associated with the seasons and/or Lake Superior’s influences. Wind rose diagrams show that prevailing winds during the summer season are stronger and more westerly than the more NW winds during the winter (Figs. 12a-b and 13a-b). This condition may have some relevance with several gravel pits located to the west of the NRRI that only operate during the summer season.
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Minneapolis – University of Minnesota Mechanical Engineering Building Late in 2010, the decision was made to add a third background site strictly for comparative purposes. The Minneapolis site was sampled a total of six times between February and June 2011, with three PM samples each in winter and summer seasons, respectively.
Weather Conditions Wind direction and precipitation data obtained during sampling periods at the Minneapolis University of Minnesota Mechanical Engineering Building sampling site are illustrated in Figure 15a-b (winter season) and Figure 16a-b (summer season). For the winter season, winds were dominantly from the east-northeast to east, whereas in the summer season, winds were generally from the east to east- southeast (Figs. 15a, 16a). During the winter season, winds greater than 1.8 m/s (4 miles per hour) were blowing approximately 38% of the time; during summer, winds greater than 1.8 m/s were also blowing approximately 38% of the time (Table 31). Measurable precipitation occurred approximately 9.3% of the time during the winter season sampling events; during the summer season, measurable precipitation also occurred during approximately 9.3% of the time air sampling occurred (Figure 15b, 16b).
Seasonal Comparisons The MOUDI totals ranged from a high of 19.23 µg/m3 from series 2331 during the summer to a low of 11.19 µg/m3 from series 2321 during the winter (Table 13). MOUDI total PM concentrations ranged from 14.11 µg/m3 to 19.23 µg/m3 in summer, and 11.19 µg/m3 to 15.29 µg/m3 during the winter (Table 13). Figure 17a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for winter (3 samples) and summer (3 samples) collected at the Minneapolis University of Minnesota Mechanical Engineering Building background site. Both graphs display clear bimodal distribution with higher concentrations of PM in the “accumulation” mode (< PM1). Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the seasonal differences in PM of the Minneapolis University of Minnesota Mechanical Engineering Building sampling site showed no significant seasonal differences (Table 25). The average MOUDI total PM concentration for all samples collected at the Minneapolis background site (15.25 µg/m3) was the highest average MOUDI total concentration obtained from sampling of the five MIR communities and the three background sites. This total was 10–28% greater than the average MOUDI total PM concentrations obtained at the other community/background sampling locations. For reference, the average MOUDI total PM obtained for all samples at the Minneapolis background site was approximately 20% higher than the average MOUDI total PM identified for all samples identified in Virginia, which had the highest average of MOUDI total for the MIR communities. Average MOUDI total PM concentrations at the Minneapolis background site were found to be 13.25 µg/m3 (winter samples) and 17.25 µg/m3 (summer samples; Tables 19 and 20). These values compare to average MOUDI total PM concentrations obtained during winter sampling from the five MIR communities (12.02 µg/m3) and three background sites (8.70 µg/m3), as well as to average MOUDI total PM concentration obtained during summer sampling from the five MIR communities (10.09 µg/m3) and three background sites (11.68 µg/m3; Table 20).The summer average MOUDI total PM concentration obtained from Minneapolis was the highest average MOUDI total PM concentration obtained from community/ background sampling locations during the study.
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Figure 15a-b. Minneapolis – University of Minnesota Mech. Eng. Building winter season wind and precipitation composites.
Figure 16a-b. Minneapolis – University of Minnesota Mech. Eng. Building summer season wind and precipitation composites.
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(a)
(b)
Figure 17a-b. Comparison of averaged MOUDI stages from Minneapolis UMN Mech. Eng. Background Site by winter season (3 samples) and summer season (3 samples). Bars = St. Dev.
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3 The Minneapolis site had the highest average PM2.5 concentration (9.73 µg/m ) for all samples collected regardless of season (Table 20). This result is not surprising, given that the Minneapolis site also had the highest average MOUDI total. This compares with the average PM2.5 fraction of the MOUDI totals for samples obtained from the five MIR communities (6.61 µg/m3) and the three background 3 sampling sites (6.49 µg/m ). The average PM2.5 fraction of MOUDI totals by season at the Minneapolis sampling site were 8.42 µg/m3 (winter) and 11.04 µg/m3 (summer; Table 20). This compares with the average PM2.5 fraction of the MOUDI totals obtained during the winter at the five MIR communities 3 3 (7.31 µg/m ) and the three background sampling sites (6.12 µg/m ), and the average PM2.5 fraction of the MOUDI totals obtained during the summer at the five MIR communities (6.09 µg/m3) and the three background sampling sites (6.94 µg/m3). The average percent PM2.5 fraction obtained for all samples collected at the Minneapolis background sampling site was 63.5%. This compares with the average PM2.5 fraction obtained for all samples from the five MIR communities (61.1%) and the three background communities (67.2%); Table 20). The average percent PM2.5 fraction obtained for samples collected at the Minneapolis background sampling site during the winter season was 62.7%. This compares with the average PM2.5 fraction obtained for samples collected during the winter season from the five MIR communities (62.4%) and the three background communities (72.5%; Table 20). The average percent PM2.5 fraction obtained for samples collected at the Minneapolis background sampling site during the summer season was 64.3%. This compares with the average PM2.5 fraction obtained for samples collected during the summer season from the five MIR communities (60.1%) and the three background communities (61.0%; Table 20). Wind patterns and precipitation data collected while conducting sampling at the Minneapolis background site can be found in Figs. 15a-b and 16a-b).
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MIR Community Locations
Keewatin Elementary School
Sample Site Location Information The rooftop sample site at the Keewatin Elementary School is approximately one mile southwest of the Keetac Taconite Processing Plant, which occurs between azimuth angles of 018º and 060º. Between azimuth angles 103° and 184° to the southeast of the school at a distance ranging from one to four miles are the Keetac mine’s tailings basin and stock piles. To the north and west of the school are the Keetac mine pits and waste rock piles ranging from 0.75 to 1.0 miles and between azimuth angles of 262º and 018º (Fig. 18).
Weather Conditions Wind direction data obtained during sampling periods at the Keewatin community sampling site are illustrated in Figures 19a-b (inactive plants), 20a-b (active plants), 21a-b (winter season) and 22a-b (summer season). Summary data for the weather conditions that existed during each sampling campaign at the Keewatin sampling location are found in Table 32, including the season, local plant activity, percentage of time winds were from the direction of the local taconite processing plant (Plant), percentage of time winds were from the direction of the local taconite mine(s) (Mine), the percentage of the sampling period during which precipitation was occurring (PCF), and the Taconite Particle Source Index (TPSI) calculated for each sampling series. At Keewatin, the TPSI indices ranged from a low of 21% during the sample series 791 (summer, inactive) to a high of 74% during the sample series 441 (winter, inactive; Table 32). An overall average TPSI for all samples collected at Keewatin regardless of season or plant activity was 46%, with seasonal TPSI averages of 53.7% in winter versus 41.5% in summer. The higher winter season TSPI most probably reflects the prevailing winds from the NW (from the direction of the mine), rather than from the SW (no sources), during the summer season (Fig. 18; Figs. 21ab and 22ab). Three of the four summer season samples had influences of precipitation that reduced the overall TPSI. Summer sample series 2201 had the highest percentage of wind from the direction of the Keetac plant facility; this amount was 6% of the sample collection time. Average TPSI values for samples collected during taconite plant/mine and mine infrastructure inactivity was 45.8%, whereas the average TPSI for samples collected while taconite plants/mines were active was 52.0% (Table 32). TPSI values were also calculated for NRRI sampling events that occurred when plants/mines were active and for when plants/mines were inactive for each of the sampling seasons. The average TPSI obtained in Keewatin during winter season when plants were inactive was 53.7%. The average TPSI obtained in Keewatin during winter season when plant/mines were active was 38.0%. The average TPSI obtained in Keewatin during summer season when plants/mines were active was 52.0%. The TPSI could not be calculated for situations when plants/mines were inactive during the summer season, as no samples were collected in Keewatin during these conditions (Table 32).
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Figure 18. Air photo of the Keewatin, MN community PM sampling site with respect to the taconite mines and processing facilities.
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Figure 19a-b. Keewatin Elementary School inactive local plant wind and precipitation composites.
Figure 20a-b. Keewatin Elementary School active local plant wind and precipitation composites.
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Figure 21a-b. Keewatin Elementary School winter season wind and precipitation composites.
Figure 22a-b. Keewatin Elementary School summer season wind and precipitation composites.
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Table 32. TPSI calculation for Keewatin Elementary School. Sample Season Activity Plant Mine PCF TPSI Series 421 W I 0 29 0 29 Series 441 W I 1 73 0 74 Series 511 W I 0 58 0 58 Series 791 S I 0 22 1 21 Series 981 S I 0 60 10 50 Series 1011 S I 0 51 8 43 Series 2201 S A 6 55 9 52 Where: TPSI = Taconite Particle Source Index (as a % of total sample time where wind is from potential sources). PCF = Precipitation Correction Factor (subtracted from “Plant” + “Mine” sources to derive TPSI).
Maximum Minimum Median Average Standard Deviation Winter Samples 74 29 58 53.7 18.6 Summer Samples 52 21 46.5 41.5 12.3 Inactive Samples 74 21 46.5 45.8 17.6 Active Samples 52 52 52 52.0 0.0
Maximum Minimum Median Average Standard Deviation Winter Inactive 74 29 58 53.7 18.6 Summer Inactive NA NA NA NA NA Winter Active 50 21 43 38.0 12.4 Summer Active 52 52 52 52.0 0.0
Statistical analyses comparing PM concentrations with TPSI indices show no significant correlation of PM1, PM2.5, PM10, or MOUDI PM totals with the TPSI at Keewatin (see statistical analyses, Table 30). Figure 23 depicts the comparison of the TPSI in Keewatin with PM concentrations. The x-y line graph shows the lack of correlation of the TPSI with the gravimetric measurements. Statistical regressions of the data indicate a lack of significant (R2) correlation values (0.25, 0.26, 0.21, and 0.09, respectively). The regression p-values are the highest of any of the MIR communities and confirm the lack of statistical significance between the TPSI and measured PM concentrations in the community. When compared with the local Keetac processing plant closure, all but sample series 2201 were collected during times of total plant shutdown. Of the six taconite processing plants in northeastern Minnesota, Keetac was shut down for the longest period of time, between mid-December 2008 through December 2009 (see Influences of Plant Activity Discussion, this report). Wind speed and wind direction measured during sampling events indicate that most of the winds in Keewatin during the NRRI sampling events were sourced from directions producing an average TPSI of ~45% from mining-related sources. Wind measured during active mining (Fig. 20ab) showed substantial winds from the direction of the Keetac open pit mine and associated mine roads, but the concentrations of PM were not statistically significant with respect to TPSI (Table 30). The two predominant wind directions displayed by the seasonal rose diagrams (Figs. 21ab–22ab) show winds that were fairly consistent from the directions of the taconite processing and mining sources, including the open pit mines and associated roads to the NW and the tailing basin and its roads to the south. Statistical analysis indicates a lack of significant correlation between the TPSI and the amounts of PM measured at the Keewatin Elementary School.
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Keewatin Elementary School Taconite Particle Source Index (TPSI) 80 40
TPSI PM1 ]
PM2.5 )
70 3 PM10 MOUDI-T
60 30
50
40 20 [Weight / Volume Air (µg/m TPSI (%)
30 , MOUDI-T 10
20 10 , PM 2.5 ,PM 1 10 PM
0 0
Series 421 Series 441 Series 511 Series 791 Series 981 Series 1011 Series 2201 Sample Series Events
Figure 23. Comparison of TPSI to PM concentrations by sample event at the Keewatin site.
During the winter and summer sampling seasons, wind directions measured at the Keewatin community sampling site were from the northwest and west, respectively; however, for samples collected during the summer sampling season, there also seems to be a southern component (Figs. 19a and 20a). Predominant winds from these directions pass over the Keetac Mine and associated mining infrastructure, with a smaller proportion of the wind vector measurements indicating winds sourced from the directions of the Keetac Taconite Plant or the Keetac tailings basin to the SE (Fig. 18). During the winter season, winds greater than 1.8 m/s (4 miles per hour) were blowing approximately 66% of the time; during summer, winds greater than 1.8 m/s were blowing approximately 59% of the time (Table 31). No measurable precipitation occurred during the winter season sampling events in Keewatin. During summer season sampling events in Keewatin, measurable precipitation occurred approximately 3.8% of the time period that air sampling occurred (Figs. 19b, 20b). During periods of time that sampling took place while local taconite plants/mines were inactive, winds were primarily from the west-northwest (Fig. 19a), from the direction of the Keetac open pit mine and mine roads (Fig. 18). During sampling events when local taconite processing/mines were inactive, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants ranged from 0% to 1%, and the percentage of time that winds (> 1.8 m/s) were sourced from the vicinity
NRRI/RI-2019/30 – Community Gravimetric Analysis 83 of the Keetac Mine infrastructure ranged from 22% to 73% (Table 32). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were inactive was 56.5% (Table 31). The overall percentage of time during which measurable precipitation was occurring regardless of wind speed for all community sampling events in Keewatin that were obtained while taconite processing plants/mines were inactive was approximately 4.5% (Fig. 19b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from a potential processing plant/mine source (PCF) obtained when taconite processing plants/mines were inactive ranged from 0% to 10% (Table 32) for individual sampling series. During the single sampling campaign that took place at Keewatin while local taconite plants/mines were active, winds were primarily from the north, northwest, and south (Fig. 20a). North and northwest winds were from the direction of the Keetac open pit mine and mine roads; winds from the south may marginally come from the direction of the westernmost parts of the Keetac tailings basin (Fig. 18). During the single sampling event when local taconite processing/mines were active, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants or mines was 6%, and the percentage of time that winds (> 1.8 m/s) were sourced from the vicinity of Keetac Mine infrastructure was 55% (Table 32). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were active was 80.2% (Table 31). The overall percentage of time during which measurable precipitation occurred during air sampling at Keewatin while taconite processing plants/mines were active was approximately 1% (Fig. 20b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from a potential processing plant/mine source (PCF) that were obtained for the single sampling event when taconite processing plants/mines were active was 9% (Table 32).
Seasonal Comparisons A total of seven PM sample series (three winter and four summer) were collected on the rooftop of Keewatin Elementary School between January 2009 and September 2010 (Table 14 and Table 32). MOUDI total concentrations range from a high of 13.49 μg/m3 in series 511 (winter season, inactive) to a low of 6.20 μg/m3 in series 421 (winter season, inactive). Figure 23a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for winter (3 samples) and summer (4 samples) collected at the Keewatin sampling site. Both graphs display bimodal distribution with clearly higher concentrations of PM in the “accumulation” mode (< PM1) during the winter season but just slightly higher concentrations (< PM1) during the summer season. Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the seasonal differences in PM of the Keewatin Elementary School site showed no significant seasonal differences (Table 25). The average MOUDI total concentration for all samples (winter and summer seasons, active and inactive) collected at Keewatin is 9.07 µg/m3, which is lower than the average MOUDI total for all samples obtained from the five MIR communities (10.92 µg/m3; Tables 19–22). The average MOUDI total concentration for samples collected during the winter season at Keewatin is 9.00 µg/m3, which is lower than the average MOUDI total concentration for samples collected during the winter season from the five MIR communities (12.02 µg/m3; Tables 19 and 20). The average MOUDI total concentration for samples collected during the summer season at Keewatin was 9.12 µg/m3, which is lower than the average MOUDI total concentration collected during the summer season from the five MIR communities (10.09 µg/m3; Tables 19 and 20).
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3 The average PM2.5 fraction (concentration) for the Keewatin site for all samples was 6.54 µg/m , which is lower than the average PM2.5 concentration for all samples collected from the five MIR 3 communities (6.61 µg/m ; Table 20). The average PM2.5 concentration for samples collected during 3 winter season at Keewatin was 6.95 µg/m , which is lower than the average PM2.5 concentration for 3 samples collected from the five MIR communities (7.31 µg/m ; Table 20). The average PM2.5 concentration for samples collected during the summer season at Keewatin was 6.23µg/m3, which is higher than the average PM2.5 concentration for samples collected during the summer season from the five MIR communities (6.09 µg/m3; Table 20). The average PM2.5 percentage relative to the MOUDI total PM collected at Keewatin for all samples is 72.5%, which is higher than the average PM2.5 percentage collected from all samples from the five MIR communities (61.1%; Table 20). In fact, the average PM2.5 percentage for all samples collected at Keewatin was the highest PM2.5 percentage obtained from the five MIR communities. The average PM2.5 percentage for samples collected from Keewatin during the winter season was 79.0%, which is higher than the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (62.4%; Table 20). The average PM2.5 percentage for samples collected from Keewatin during the winter season was 67.6%, which is higher than the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (60.1%; Table 20).
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(a)
(b)
Figure 24a-b. Comparison of averaged MOUDI stages from Keewatin Elementary School Site by winter season (3 samples) and summer season (4 samples). Bars = St. Dev.
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Local Mine/Plant Activity A prolonged shutdown at the Keetac mine and plant allowed only one of the seven samples collected at the Keewatin Elementary School to be obtained during active mining/processing. The representativeness of this single sample during active mining/processing at Keewatin cannot be fully understood based on the limited sampling that could be achieved during this study, and the results summarized below must be understood in the context of this limited sampling. The MOUDI total concentration for the single sample obtained at Keewatin while processing plants/mines were active was 6.55 µg/m3. The MOUDI total concentrations for the six samples obtained from Keewatin while local processing plants/mines were inactive ranged from 6.2 µg/m3 to 13.49 µg/m3 (Table 14). Figure 24a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for periods where local taconite processing plants/mines were inactive (6 samples) and periods where local taconite processing plants/mines were active (1 sample) that were collected at the Keewatin sampling site. Both graphs display faint bimodal distribution with slightly higher concentrations of PM in the “accumulation” mode (< PM1). Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM, with the exception of sampling that occurred during active plant/mine, due to only one sample being collected. For this reason, statistical analysis of the differences in PM of the Keewatin Elementary School site based on local plant/mine activity could not be conducted and was omitted from Table 28. The average MOUDI total PM concentration for all samples collected at Keewatin during processing plant/mining inactivity was 9.49 µg/m3, which is lower than the average MOUDI total PM concentration for samples collected from the five MIR communities while processing plant/mining was inactive (10.31 µg/m3; Tables 21 and 22). The MOUDI total PM concentration for the single sample collected at Keewatin while processing plants/mines were active was 6.55 µg/m3, which is less than the average MOUDI total PM concentration for samples collected from the five MIR communities during processing plant/mining activity (11.52 µg/m3; Table 21). Keewatin had the greatest difference between average MOUDI total PM concentrations for situations where average MOUDI total PM concentrations were greater during inactive versus active mining. The average PM2.5 concentration for samples collected at Keewatin during processing plant/mining 3 inactivity was 6.92 µg/m , which is higher than the average PM2.5 concentration for samples collected during processing plant/mining inactivity in the five MIR communities (6.39 µg/m3; Table 22). The average PM2.5 concentration for the single sample (Series 2201) collected at Keewatin during processing 3 plant/mining activity was 4.27 µg/m , which is lower than the average PM2.5 concentration for all samples collected from the five MIR communities during processing plant/mining activity (6.83 µg/m3). The average PM2.5 percent fraction for all samples collected at Keewatin was 72.5%, which is higher than the average PM2.5 percent fraction for all samples collected from the five MIR communities (61.1%; Table 22). The average PM2.5 percent fraction for samples collected at Keewatin while processing plants/mining were inactive was 73.7%, which is higher than the average PM2.5 percent fraction for samples collected during processing plant/mining inactivity at the five MIR communities (62.1%; Table 22). The average PM2.5 percent fraction for samples collected at Keewatin while processing plant/mining was active was 65.1%, which is higher than the average PM2.5 percent fraction for samples collected during processing plant/mining activity from the five MIR communities (60.1%; Table 22).
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(a)
(b)
Figure 25a-b. Comparison of averaged MOUDI stages from Keewatin Elementary School during local mine/plant Inactivity (6 samples) and Activity (1 sample). Bars = St. Dev.
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Hibbing High School
Sample Site Location and Weather Conditions Hibbing High School is located within a six-mile radius of two taconite processing plants and numerous mine pits, tailings basins, and waste piles (Fig. 26). The Hibbing Taconite Plant (Hibtac) is located north-northwest of the Hibbing High School PM sampling location between azimuth angles of 328º and 339º at a distance of approximately four miles. The previously mentioned Keetac Taconite Plant is located west of Hibbing High School between azimuth angles of 259º and 267º at a distance of approximately six miles. Mine pits and waste rock piles from the two facilities range in distance from 2.5 to 6.0 miles and between azimuth angles of 267º and 328º, and between 339º and 13º from Hibbing High School (Fig. 26).
Weather Conditions Wind direction data obtained during sampling periods at the Hibbing community sampling site are illustrated in Figures 27a-b (inactive plants), 28a-b (active plants), 29a-b (winter season), and 30a-b (summer season). Summary data for the weather conditions that existed during sampling at the Hibbing sampling location are found in Table 33, including the season, local plant activity, percentage of time winds were from the direction of the local taconite processing plant (Plant), percentage of time winds were from the direction of the local taconite mine(s) (Mine), the percentage of the sampling period during which precipitation was occurring (PCF), and the Taconite Particle Source Index (TPSI) calculated for each sampling series. Weather data collected from the Hibbing High School MIR community sampling site showed potential for inputs of PM from the surrounding mining activities based on prevailing wind directions recorded at the time of sampling and produced an average ~36% TPSI. A total of nine samples (four winter season and five summer season) were collected during an 18-month period and are listed along with their respective TPSI values in Table 33. The TPSI indices averaged 37% overall by both seasons and ranged from a low of 13% for sample series 781 (summer, inactive) to a high of 57% for sample series 451 (winter, active). The majority of wind was from the direction of mining-related sources (270° to 0.00°), including wind from the direction(s) of one or both taconite processing plants (see Figs. 27ab and 28ab). Winter sample series 681 had the highest percentage of wind (13%) from the direction of the Hibtac plant. Three of the nine samples had measurable precipitation during periods of time that winds were greater than 1.8 meters/second (PCF) that impacted TPSI values. Statistical analyses comparing PM concentrations with TPSI indices that show no statistically significant correlation of PM1, PM2.5, PM10, or MOUDI totals with the TPSI at the Hibbing site (see statistical analyses, Table 25). A graphical portrayal of this relationship is shown in Figure 31. Regression analysis comparing PM1, PM2.5, PM10, and MOUDI-T with the TPSI indicate low values of statistical correlation, as reflected by the low (R2) correlation values of 0.00, 0.26, 0.30, and 0.09, respectively. As indicated in Table 33, contributions to the TPSI in Hibbing are most influenced by values reflecting the percentage of time that winds with speeds > 1.8 meters/second were measured in a direction from a potential mine or mine infrastructure source relative to a potential taconite process plant facility. The percentage of winds from the directions of plants relative to winds from the directions of both plant and mining infrastructure ranged from 2.3% to 31.7%. Since most of the wind that resulted in a higher TPSI is from the direction of the mines, influence on the overall TPSI from the plants is smaller. Although seven of the nine samples showed some wind from the directions of plants, the percentages of time that the wind was blowing greater than 1.8 meters per second relative to the overall sample acquisition duration were relatively low (≤ 13%). There was little difference in the TPSI with regard to mine/plant activity, with an average TPSI 35% for periods where taconite plants and/or mines were inactive versus an average TPSI of 38% for periods where taconite plants and/or mines were active.
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Figure 26. Air photo of the Hibbing, MN community PM sampling site with respect to the taconite mines and processing facilities.
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Figure 27a-b. Hibbing High School inactive local plant wind and precipitation composites.
Figure 28a-b. Hibbing High School active local plant wind and precipitation composites.
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Figure 29a-b. Hibbing High School winter season wind and precipitation composites.
Figure 30a-b. Hibbing High School summer season wind and precipitation composites.
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Table 33. TPSI calculation for Hibbing High School. Sample Season Activity Plant Mine PCF TPSI Series 451 W A 2 55 0 57 Series 521 W A 0 15 0 15 Series 631 W A 6 39 0 45 Series 681 W A 13 28 11 30 Series 711 S A 3 37 0 40 Series 721 S A 9 31 1 39 Series 781 S I 3 10 0 13 Series 971 S I 9 48 5 52 Series 1001 S I 0 49 10 39 Where: TPSI = Taconite Particle Source Index (as a % of total sample time where wind is from potential sources). PCF = Precipitation Correction Factor (subtracted from “Plant” + “Mine” sources to derive TPSI).
Maximum Minimum Median Average Standard Deviation Winter Samples 57 15 37.5 36.8 15.8 Summer Samples 52 13 39 36.6 12.8 Inactive Samples 52 13 39 34.7 16.2 Active Samples 57 15 39.5 37.7 13.0
Maximum Minimum Median Average Standard Deviation Winter Inactive NA NA NA NA NA Summer Inactive 57 15 37.5 36.8 15.8 Winter Active 52 13 39 34.7 16.2 Summer Active 40 39 39.5 39.5 0.5
The Keetac plant/mine may also have been an influence in TPSI calculations at the Hibbing sample site. The Keetac mine and plant, which is more than six miles to the west, was shut down during the collection of all nine samples at the Hibbing High School site. The last three summer samples (series 781, 971, and 1001) were collected during both Keetac and Hibtac closures. Prevailing winds during the winter at Hibbing are mostly N to NW. During the summer, prevailing wind directions change to more westerly directions (Figs. 29ab–30ab), indicating potential PM contributions from the Hibtac mine and associated mine infrastructure. Samples collected when the mine/plant were active do show predominant winds from the directions of both Hibtac’s mine and plant (Fig. 28ab); however, the concentrations of PM were not statistically significant with respect to the calculated TPSI (Table 33).
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Hibbing High School Taconite Particle Source Index (TPSI) 80 40
TPSI PM1
PM2.5 )] 70 3 PM10 MOUDI-T
60 30
50 [Weight / Volume Air (µg/m 40 20 TPSI (%)
30 , MOUDI-T 10
20 10 , PM 2.5 , PM 1 10 PM
0 0
Series 451 Series 521 Series 631 Series 681 Series 711 Series 721 Series 781 Series 971 Series 1001 Sample Series Events
Figure 31. Comparison of TPSI to PM concentrations by sample event at the Hibbing site.
During the winter sampling season, wind directions measured at the Hibbing community sampling site were primarily from the north and northwest (Fig. 29a). Winter season winds from these directions would be from the direction of the Hibtac open pit mine and associated mining infrastructure (Fig. 26). During the winter sampling season, winds greater than 1.8 m/s (4 miles per hour) were blowing 75% of the time. During the summer sampling season, wind directions measured at the Hibbing community sampling site were primarily from west and northwest, respectively (Fig. 30a). Predominant winds observed during summer sampling would be from the directions of the Keetac open pit and associated mining infrastructure (west winds) as well as from the direction of the Hibtac open pit mine and associated infrastructure (Fig. 26). During the summer sampling season, winds greater than 1.8 m/s were blowing approximately 62% of the time (Table 31). Measurable precipitation occurred less than 1% of the time during the winter season sampling events in Hibbing (Figure 29b). During the summer season sampling events in Hibbing, measurable precipitation occurred approximately 4.1% of the time period during which air sampling occurred (Fig. 30b).
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During periods of time that air sampling took place at Hibbing while local taconite plants/mines were inactive, winds were primarily from the west, with winds less commonly blowing from northwest and southwest directions (Fig. 27a). The winds directions measured during periods of taconite plant/mine inactivity at Hibbing would have been from the directions of the Keetac and Hibtac open pit mines and associated mining infrastructure (Fig. 26). During sampling events when local taconite processing/mines were inactive, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants ranged from 0% to 9%, and the percentage of time that winds (> 1.8 m/s) were sourced from the directions of local mines and associated mining infrastructure ranged from 10% to 49% (Table 33). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were inactive was 53.7% (Table 31). The overall percentage of time during which measurable precipitation was occurring regardless of wind speed for all community sampling events in Hibbing that were obtained while taconite processing plants/mines were inactive was approximately 7.1% (Figure 276b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from potential processing plant/mine sources (PCF) obtained when taconite processing plants/mines were inactive ranged from 0% to 10% (Table 33) for individual sampling series. During periods of time that air sampling that took place at Hibbing while local taconite plants/mines were active, winds were primarily from the north and northwest, with fewer occurrences of winds from the southeast (Figure 28a). Winds from the north would have been from the direction of the Hibtac taconite processing plant and Hibtac Mine and associated mining infrastructure, whereas winds from the northwest would have been from the direction of the Hibtac Mine and associated mining infrastructure (Fig. 26). Winds from the southeast would be from a direction where no local mining infrastructure occurs. During sampling events when local taconite processing/mines were active, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants ranged from 0% to 13%, and the percentage of time that winds (> 1.8 m/s) were sourced from local mines and associated mining infrastructure ranged from 15% to 55% (Table 33). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were active was 74% (Table 31). The overall percentage of time during which measurable precipitation occurred during air sampling at Hibbing while taconite processing plants/mines were active was approximately 1% (Fig. 28b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from a potential processing plant/mine source (PCF) that were obtained during air sampling at Hibbing when taconite processing plants/mines were active ranged from 0% to 11% (Table 33).
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Seasonal Comparisons Four winter season and five summer season PM sample series were collected on the Hibbing High School rooftop between February 2009 and August 2009 (Table 15). MOUDI total concentrations ranged from a high of 15.20 µg/m3 from sample series 521 (winter, active) to a low of 6.01 µg/m3 for sample series 1001 (summer, inactive; Table 15). MOUDI total concentrations for samples taken during the summer season ranged from 6.01 µg/m3 to 14.15 µg/m3. MOUDI total concentrations for samples taken during the winter season ranged from 8.32 µg/m3 to 15.2µg/m3 (Table 15). Figure 32a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for winter (4 samples) and summer (5 samples) collected at the Hibbing High School site. Both graphs display clear bimodal distribution with higher concentrations of PM in the “accumulation” mode (< PM1) during the winter season, as opposed to slightly higher concentrations (> PM1) during the summer season. Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the seasonal differences in PM of the Hibbing High School site showed no significant seasonal differences (Table 25). The average MOUDI total concentration for all samples was 10.61 µg/m3 (Tables 19–22), which is less than the overall MOUDI total average for all samples from the five MIR communities (10.92 µg/m3; Tables 19 and 20). The average MOUDI total concentration for samples collected during the winter season at Hibbing is 11.57 µg/m3, which is lower than the average MOUDI total concentration for samples collected during the winter season from the five MIR communities (12.02 µg/m3; Tables 19 and 20). The average MOUDI total concentration for samples collected during the summer season at Hibbing was 9.84 µg/m3, which is lower than the average MOUDI total concentration collected during the summer season from the five MIR communities (10.09 µg/m3; Tables 19 and 20). 3 The average PM2.5 fraction (concentration) for the Hibbing site for all samples is 6.45 µg/m , which is lower than the average PM2.5 concentration for all samples collected from the five MIR communities 3 (6.61 µg/m ; Table 20). The average PM2.5 concentration for samples collected during winter season at 3 Hibbing was 7.18 µg/m , which is lower than the average PM2.5 concentration for samples collected from 3 the five MIR communities (7.31 µg/m ; Table 20). The average PM2.5 concentration for samples collected 3 during the summer season at Hibbing was 5.87 µg/m , which is lower than the average PM2.5 concentration for samples collected during the summer season from the five MIR communities (6.09 µg/m3; Table 20). The average PM2.5 percentage relative to the MOUDI total PM collected at Hibbing for all samples is 61.2%, which is higher than the average PM2.5 percentage collected from all samples from the five MIR communities (61.1%; Table 20). The average PM2.5 percentage for samples collected from Hibbing during the winter season was 62.3%, which is approximately equal to the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (62.4%; Table 20). The average PM2.5 percentage for samples collected from Hibbing during the winter season was 60.3%, which is higher than the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (60.1%; Table 20).
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(a)
(b)
Figure 32a-b. Comparison of averaged MOUDI stages from Hibbing High School Site by winter season (4 samples) and summer season (5 samples). Bars = St. Dev.
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Local Mine/Plant Activity Of the nine samples collected at Hibbing, three were during inactive and six were during active mining (Table 15). MOUDI total concentrations during plant activity range from a high of 13.49 μg/m3 in series 511 (winter season, inactive) to a low of 6.20 μg/m3 in series 421 (winter season, inactive). MOUDI total concentrations collected in Hibbing while local processing plants/mines were inactive ranged from 6.01 µg/m3 to 14.14 µg/m3. MOUDI total concentrations collected in Hibbing while local processing plants/mines were active ranged from 7.57 µg/m3 to 15.2 µg/m3 (Table 15). Figure 33a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for periods where local taconite plants/mines were inactive (3 samples) and periods where local taconite plants /mines were active (6 samples) that were collected at the Hibbing sampling site. Both graphs display clear bimodal distribution with slightly higher concentrations of PM in the “accumulation” mode (< PM1). Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the differences in PM of the Hibbing High School site based on local plant/mine activity showed no significant differences (Table 25). The average MOUDI total concentration for all samples at Hibbing was 10.61 µg/m3 (Tables 19–22), which is lower than the average MOUDI total for all samples obtained from the five MIR communities (10.92 µg/m3; Tables 19–22). The average MOUDI total concentration for all samples collected at Hibbing during processing plant/mining inactivity was 10.76 µg/m3, which is higher than the average MOUDI total concentration for samples collected from the five MIR communities while processing plant/mining was inactive (10.31 µg/m3; Tables 21 and 22). The average MOUDI total concentration for samples collected at Hibbing while processing plants/mines were active was 10.54 µg/m3, which is less than the average MOUDI total concentration for samples collected from the five MIR communities during processing plant/mining activity (11.52 µg/m3; Tables 21 and 22). 3 The average PM2.5 concentration for all samples collected at Hibbing was 6.45 µg/m , which is lower than the average PM2.5 concentration for all samples collected from the five MIR communities 3 (6.61 µg/m ; Table 22). The average PM2.5 concentration for samples collected at Hibbing during 3 processing plant/mining inactivity was 6.75 µg/m , which is higher than the average PM2.5 concentration for samples collected during processing plant/mining inactivity in the five MIR communities (6.39 µg/m3; Table 22). The average PM2.5 concentration for samples collected at Hibbing during processing 3 plant/mining activity was 6.31 µg/m , which is lower than the average PM2.5 concentration for samples collected from the five MIR communities during processing plant/mining activity (6.83 µg/m3). The average PM2.5 percent fraction for all samples collected at Hibbing was 61.2%, which is higher than the average PM2.5 percent fraction for all samples collected from the five MIR communities (61.1%; Table 22). The average PM2.5 percent fraction for samples collected at Hibbing while processing plants/mining were inactive was 63.6%, which is higher than the average PM2.5 percent fraction for samples collected during processing plant/mining inactivity at the five MIR communities (62.1%; Table 22). The average PM2.5 percent fraction for samples collected at Hibbing while processing plant/mining was active was 60.0%, which is lower than the average PM2.5 percent fraction for samples collected during processing plant/mining activity from the five MIR communities (60.1%; Table 22).
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(a)
(b)
Figure 33a-b. Comparison of averaged MOUDI stages from Hibbing High School during local mine/plant Inactivity (3 samples) and Activity (6 samples). Bars = St. Dev.
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Virginia City Hall
Sample Site Location and Weather Conditions The city of Virginia is situated in a topographic low just south of the Laurentian Divide and is nearly surrounded by iron mining activity (Fig. 34). Similar to Hibbing, this location is within a two- to five-mile radius of two taconite processing plants and numerous mine pits and waste piles. The Minorca Taconite Plant, owned and operated by Arcelor Mittal, is located north-northeast between the azimuth angles of 011º and 045º at a distance of approximately 2.5 miles. The Thunderbird Mine (Utac), owned and operated by Cliffs Natural Resources, is located approximately 1.8 to 2.9 miles south of town between azimuths 170º and 206º. From nearly due west at an azimuth of 269º, spanning northwest to an azimuth of 335º, is a series of open mine pits, tailing basins, active waste rock piles, and associated mine haul roads owned by Minntac, which is operated by US Steel. These features are at a distance ranging from nine to two miles from the City Hall sample site located in Virginia. The Minntac Taconite Plant is northwest of the sampling site just beyond the previously mentioned pits, etc., between azimuths 298º and 311º, at a distance of approximately five miles.
Weather Conditions Wind direction data obtained during sampling periods at the Virginia community sampling site are illustrated in Figures 35a-b (inactive plants), 36a-b (active plants), 37a-b (winter season), and 38a-b (summer season). Summary data for the weather conditions that existed during sampling at the Virginia community sampling location are found in Table 34, including the season, local plant activity, percentage of time winds were from the direction of the local taconite processing plant (Plant), percentage of time winds were from the direction of the local taconite mine(s) (Mine), the percentage of the sampling period during which precipitation was occurring (PCF), and the Taconite Particle Source Index (TPSI) calculated for each sampling series. The TPSI was calculated for 10 samples collected in Virginia. These samples include five samples each for winter and summer seasons (Table 34). The calculated TPSI indices for the individual sampling events at Virginia range from a low of 20% during the summer (sample series 801) to a high of 72% during the winter (sample series 311), and average ~38% overall. By season, the average TPSI for samples collected during the winter season (41%) was slightly higher than the average TPSI for samples collected during the summer season (36%). The percentage of winds > 1.8 meters/second from the directions of plants relative to winds > 1.8 meters/second from the directions of both plant and mining infrastructure ranged from 6.3% to 87.5%. All but two of the samples (sample series 501 and sample series 621; Table 34) had the majority of winds sourced from the direction the mines versus the directions of the taconite plants; both of those samples occurred in the winter season. All five winter sample series had significant winds coming from the directions of the taconite processing plants, with the highest occurring during sample series 621, at 29%. There were also minimal influences of precipitation (PCF), with only one sample having greater than 1%. Statistical analyses comparing PM concentrations with TPSI indices show statistically significant correlation of PM1, PM2.5, PM10, and also the MOUDI totals with TPSI (see statistical analyses, Table 25). The p-values generated in TPSI/PM regressions are all less than 0.05, thereby rejecting the null hypothesis. A moderate amount of correlation between the PM fractions can also be seen from the x-y line graph in Figure 39. This relationship is further supported by regression analysis of the data that resulted in the highest (R2) correlation values of MIR communities in the study—0.46, 0.53, 0.49, and 0.37, respectively. The Virginia site was one of two sites of the five MIR communities where the TPSI and PM concentrations within the community were found to be statistically significant.
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Figure 34. Air photo of the Virginia, MN community PM sampling site with respect to the taconite mines and processing facilities.
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Figure 35a-b. Virginia City Hall inactive local plant wind and precipitation composites.
Figure 36a-b. Virginia City Hall active local plant wind and precipitation composites.
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Figure 37a-b. Virginia City Hall winter season wind and precipitation composites.
Figure 38a-b. Virginia City Hall summer season wind and precipitation composites.
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Table 34. TPSI calculation for Virginia City Hall. Sample Season Activity Plant Mine PCF TPSI Series 311 W A 17 55 0 72 Series 471 W A 8 23 4 27 Series 501 W A 21 3 0 24 Series 571 W A 9 20 0 29 Series 621 W A 29 22 0 51 Series 801 S I 4 16 0 20 Series 811 S I 4 20 1 23 Series 931 S I 4 44 0 48 Series 961 S I 6 38 1 43 Series 991 S A 3 44 0 47 Where: TPSI = Taconite Particle Source Index (as a % of total sample time where wind is from potential sources). PCF = Precipitation Correction Factor (subtracted from “Plant” + “Mine” sources to derive TPSI).
Standard Maximum Minimum Median Average Deviation Winter Samples 72 24 29 40.6 18.4 Summer Samples 48 20 43 36.2 12.2 Inactive Samples 48 20 43 36.2 12.2 Active Samples 72 24 38 41.7 16.9
Maximum Minimum Median Average Standard Deviation Winter Inactive NA NA NA NA NA Summer Inactive 72 24 29 40.6 18.4 Winter Active 48 20 33 33.5 12.2 Summer Active 47 47 47 47 47
When plant closure is considered, the relationship between PM concentrations and TPSI makes more sense. The six active samples, which are predominantly from the winter season, have an average TPSI of 41.7% (Table 34). This relationship seemingly reflects the predominant NW prevailing winds (most common in the winter) from the directions of the Minntac mine, plant, tailings basin, and associated haul roads (Fig. 37ab). Likewise, most of the samples obtained during periods of taconite processing plant/mine inactivity are from the summer season, where prevailing winds are less likely to intersect a potential source (Fig. 38ab). For comparison, the inactive average TPSI is slightly lower at 33.5%. However, since only one of the summer sample series were collected during periods of taconite plant/mine activity, it is difficult to conclude this relationship. Similar to the other MIR communities, wind rose diagrams show that prevailing winds during the winter are more commonly from the northwest direction compared to more westerly direction during the summer season (Figs. 37ab–38ab). Because of the prevailing winds, potential mine-related PM is more likely to come from the direction of Minntac’s mine and plant than from the direction of the Minorca mine and taconite processing plant to the northeast, or from the direction of Utac’s Thunderbird mine and primary crusher to the south.
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Virginia City Hall Taconite Particle Source Index (TPSI) 80 40
TPSI PM1
PM2.5 )] 70 3 PM10 MOUDI-T
60 30
50 [Weight / Volume Air (µg/m 40 20 TPSI (%)
30 , MOUDI-T 10
20 10 , PM 2.5 , PM 1 10 PM
0 0 Series 811 Series 991 Series 801 Series 961 Series 931 Series 501 Series 471 Series 621 Series 311 SampleSeries 571 Series Events Figure 39. Comparison of TPSI to PM concentrations by sample event at the Virginia site.
The statistically significant correlation between PM concentrations and the TPSI suggest that the amount of PM in aerosol samples collected at the Virginia MIR community sampling site may have been influenced by taconite processing plant/mining activities. During the winter sampling season, wind directions measured at the Virginia community sampling site were primarily from the northwest (Fig. 37a). Winter season winds from this direction would be from the direction of the Minntac taconite processing plant and open pit mine and associated mining infrastructure (Fig. 34). During the winter sampling season, winds greater than 1.8 m/s (4 miles per hour) were blowing 76.6% of the time; during the summer sampling season, winds greater than 1.8 m/s were blowing approximately 54.7% of the time (Table 31). During the summer sampling season, wind directions measured at the Virginia community sampling site were primarily from west (Fig. 38a). Predominant winds observed during summer sampling would be from the direction Minntac Taconite Mine and associated mining infrastructure of the Keetac open pit and associated mining infrastructure (west winds), with lesser winds from the northwest coming from the direction of the Minntac taconite processing plant (Fig. 34). Winds derived from the west-southwest would be from a direction where local taconite processing plant/mine and associated mining infrastructure does not exist (Fig. 34).
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Measurable precipitation occurred approximately 2.5% of the time during the winter season community sampling events in Virginia (Fig. 37b). During summer season sampling events in Virginia, measurable precipitation occurred approximately less than 1% of the time period during which air sampling occurred (Fig. 36b). During periods of time that air sampling took place at Virginia while local taconite plants/mines were inactive, winds were primarily from the west, with winds less commonly blowing from northwest and southwest directions (Fig. 35a). The winds directions measured during periods of taconite plant/mine inactivity at Virginia would have been from the directions of the Minntac Taconite processing plant (northwest) and Minntac open pit mines and associated mining infrastructure (Fig. 34). During sampling events when local taconite processing/mines were inactive, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants ranged from 4% to 6%, and the percentage of time that winds (> 1.8 m/s) were sourced from the directions of local mines and associated mining infrastructure ranged from 16% to 44% (Table 34). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were inactive was 62.8% (Table 31). The overall percentage of time during which measurable precipitation was occurring regardless of wind speed for all community sampling events in Virginia that were obtained while taconite processing plants/mines were inactive was less than 1% (Fig. 35b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from potential processing plant/mine sources (PCF) obtained when taconite processing plants/mines were inactive ranged from 0% to 1% (Table 34) for individual sampling series. During periods of time that air sampling took place at Virginia while local taconite plants/mines were active, winds were primarily from the west, with fewer occurrences of winds from the northwest (Fig. 36a). The winds directions measured during periods of taconite plant/mine activity at Virginia would have been primarily from the direction of the Minntac open pit mines and associated mining infrastructure (west), and to a lesser extent from the direction of the Minntac Taconite processing plant (northwest) (Fig. 34). Winds from the southwest, south, and southeast would be from directions where no local mining infrastructure occurs. During sampling events when local taconite processing/mines were active, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants ranged from 3% to 29%, and the percentage of time that winds (> 1.8 m/s) were sourced from local mines and associated mining infrastructure ranged from 3% to 55% (Table 34). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were active was 76.7% (Table 31). The overall percentage of time during which measurable precipitation occurred during air sampling at Virginia while taconite processing plants/mines were active was approximately 3.8% (Fig. 36b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from a potential processing plant/mine source (PCF) that were obtained during air sampling at Virginia when taconite processing plants/mines were active ranged from 0% to 4% (Table 34).
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Seasonal Comparisons A total of 10 PM sample series (five winter and five summer) were collected on the rooftop of the Virginia City Hall between November 2008 and August 2009. MOUDI totals ranged from a high of 18.01 µg/m3 in summer inactive sample series 811 to a low of 7.02 µg/m3 in winter active sample series 311 (Table 16). MOUDI totals for samples obtained from Virginia during the winter season ranged from 7.02 µg/m3 to 16.30 µg/m3. MOUDI totals for samples obtained from Virginia during the summer season ranged from 7.27 µg/m3 to 18.01 µg/m3 (Table 16). Figure 40a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for winter (5 samples) and summer (5 samples) collected at the Virginia City Hall site. Both graphs display clear bimodal distribution with slightly higher concentrations of PM in the “coarse” mode (> PM1). Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the seasonal differences in PM of the Virginia City Hall site showed no significant seasonal differences (Table 25). The average MOUDI total concentration for all samples collected in Virginia was 12.70 µg/m3 (Tables 19–22), which is higher than the overall MOUDI total average for all samples from the five MIR communities (10.92 µg/m3; Tables 19 and 20). The average MOUDI total concentration for samples collected during the winter season at Virginia is 13.46 µg/m3, which is higher than the average MOUDI total concentration for samples collected during the winter season from the five MIR communities (12.02 µg/m3; Tables 19 and 20). The average MOUDI total concentration for samples collected during the summer season at Virginia was 11.64 µg/m3, which is higher than the average MOUDI total concentration collected during the summer season from the five MIR communities (10.09 µg/m3; Tables 19 and 20). 3 The average PM2.5 fraction (concentration) for the Virginia site for all samples is 7.04 µg/m , which is higher than the average PM2.5 concentration for all samples collected from the five MIR communities 3 (6.61 µg/m ; Table 20). The average PM2.5 concentration for samples collected during winter season at 3 Virginia was 7.11 µg/m , which is lower than the average PM2.5 concentration for samples collected from 3 the five MIR communities (7.31 µg/m ; Table 20). The average PM2.5 concentration for samples collected 3 during the summer season at Virginia was 6.98 µg/m , which is higher than the average PM2.5 concentration for samples collected during the summer season from the five MIR communities (6.09 µg/m3; Table 20). The average PM2.5 percentage relative to the MOUDI total PM collected at Virginia for all samples is 55.7%, which is lower than the average PM2.5 percentage collected from all samples from the five MIR communities (61.1%; Table 20). The average PM2.5 percentage for samples collected from Virginia during the winter season was 53.8%, which is lower than the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (62.4%; Table 20). The average PM2.5 percentage for samples collected from Virginia during the winter season was 57.7%, which is lower than the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (60.1%; Table 20).
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(a)
(b)
Figure 40a-b. Comparison of averaged MOUDI stages from Virginia City Hall Site by winter season (5 samples) and summer season (5 samples). Bars = St. Dev.
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Local Mine/Plant Activity Because of Virginia’s unique geographical location in a topographical low that is surrounded by three taconite mines and accompanying processing plants, samples were designated “active” if two or more mines/plants were operating. Of the 10 samples collected at Virginia, 4 were during periods of mine inactivity and 6 were during active mining (Table 16). MOUDI total concentrations obtained in Virginia while local processing plants/mines were inactive ranged from 10.55 µg/m3 to 18.01 µg/m3. MOUDI total concentrations measured in Virginia while local processing plants/mines were active ranged from 7.02 µg/m3 to 16.30 µg/m3. Figure 41a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for periods where local taconite plants/mines were inactive (4 samples) and for periods of time when local taconite processing plants/mines were active (6 samples) that were collected at the Virginia sampling site. Both graphs display clear bimodal distribution with slightly higher concentrations of PM in the “coarse” mode (> PM1). Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the differences in PM of the Virginia City Hall site based on local plant/mine activity showed no significant differences (Table 28). The average MOUDI total concentration for all samples at Virginia was 12.70 µg/m3 (Tables 19–22), which is higher than the average MOUDI total for all samples obtained from the five MIR communities (10.92 µg/m3; Tables 19–22). The average MOUDI total concentration for all samples collected at Virginia during processing plant/mining inactivity was 13.11 µg/m3, which is higher than the average MOUDI total concentration for samples collected from the five MIR communities while processing plant/mining was inactive (10.31 µg/m3; Tables 21 and 22). The average MOUDI total concentration collected at Virginia while processing plants/mines were active was 12.43 µg/m3, which is less than the average MOUDI total concentration for samples collected from the five MIR communities during processing plant/mining activity (11.52 µg/m3; Tables 21 and 22). 3 The average PM2.5 concentration for all samples collected at Virginia was 7.04 µg/m , which is higher than the average PM2.5 concentration for all samples collected from the five MIR communities 3 (6.61 µg/m ; Table 22). The average PM2.5 concentration for samples collected at Virginia during 3 processing plant/mining inactivity was 7.69 µg/m , which is higher than the average PM2.5 concentration for samples collected during processing plant/mining inactivity in the five MIR communities (6.39 µg/m3; Table 22). The average PM2.5 concentration for samples collected at Virginia during processing 3 plant/mining activity was 6.61 µg/m , which is lower than the average PM2.5 concentration for samples collected from the five MIR communities during processing plant/mining activity (6.83 µg/m3; Table 22). The average PM2.5 percent fraction for all samples collected at Virginia was 55.7%, which is lower than the average PM2.5 percent fraction for all samples collected from the five MIR communities (61.1%; Table 22). The average PM2.5 percent fraction for samples collected at Virginia while processing plants/mining were inactive was 57.8%, which is lower than the average PM2.5 percent fraction for samples collected during processing plant/mining inactivity at the five MIR communities (62.1%; Table 22). The average PM2.5 percent fraction for samples collected at Virginia while processing plant/mining was active was 54.4%, which is lower than the average PM2.5 percent fraction for samples collected during processing plant/mining activity from the five MIR communities (60.1%; Table 22).
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(a)
(b)
Figure 41a-b. Comparison of averaged MOUDI stages from Virginia City Hall during local mine/plant Inactivity (4 samples) and Activity (6 samples). Bars = St. Dev.
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Babbitt Municipal Building
Sample Site Location and Weather Conditions The Babbitt community sample site location is located on the rooftop of the Babbitt Municipal Building, which is situated on the south end of town on South Drive. A series of mine pits, haul roads, and waste rock piles—all part of Northshore Mining Company’s Peter Mitchell Mine—are located to the south between azimuths 108º and 216º at a distance ranging from two to six miles. Unlike the other four community locations that have one or two complete taconite processing facilities within close proximity, Northshore’s processing facility for this mine is located in Silver Bay, MN, which is approximately 50 miles southeast. There is, however, a primary crusher located on the east end of the mine pit that is used to crush the ore down to the 2- to 3-inch size for rail transport down to Lake Superior. This crushing facility is also located almost straight southeast of the sample location between azimuths 131º and 143º at about 3.5 miles distance (Fig. 42).
Weather Conditions Wind direction data obtained during sampling periods at the Babbitt community sampling site are illustrated in Figures 43a-b (inactive plants), 44a-b (active plants), 45a-b (winter season) and 46a-b (summer season). Summary data for the weather conditions that existed during sampling at the Babbitt community sampling location are found in Table 35, including the season, local plant activity, percentage of time winds were from the direction of the local taconite processing plant (Plant), percentage of time winds were from the direction of the local taconite mine(s) (Mine), the percentage of the sampling period during which precipitation was occurring (PCF), and the Taconite Particle Source Index (TPSI) calculated for each sampling series. A total of seven winter and nine summer season samples were collected from the Babbitt Municipal Building rooftop. The TPSI was calculated for each using the weather data collected at the time of sampling (Table 35). The overall average TPSI of 18% was the lowest of the MIR communities and included averages of 22% in winter and 15% in summer. The indices ranged from a low of 3% during the winter sample series 371 to a high of 56% during the winter sample series 531. A fairly even mixture of winds from directions encompassing both the plant and the mine were observed, especially during the winter. The winter season sample series 671 had the most wind from the direction of the plant (primary crushing facility), which matched the amount of wind coming from the direction of the mine. Minimal influences of precipitation (PCF) were experienced at Babbitt. Analyses comparing PM concentrations with TPSI indices show statistically significant correlation of PM1, PM2.5, and PM10 with TPSI (see statistical analyses, Table 30). The x-y line graph (Fig. 47) shows minor correlation of the TPSI, supporting the statistical analyses. Regression analysis of the data result in 2 (R ) correlation values of 0.18, 0.18, 0.18, and 0.12, for PM1, PM2.5, PM10, and the TPSI. The calculated p-values were all slightly less than the 0.05 significance value cutoff. Because the Babbitt MIR community air sampling site is located north of the Northshore mine and its primary crusher, the prevailing winds during either sampling season are not likely to transport PM from any potential mining sources (Figs. 45ab–46ab). During the winter season, approximately 20% of the wind comes from the direction of the crusher and eastern end of the mine (where most of the mining activity is being conducted). There is not a statistically significant correlation between PM concentrations and the TPSI during these conditions. Winds were predominantly from the west (including NW and SW) when the active mine/plant samples were collected (Fig. 44ab) and were from a direction absent of mining-related infrastructure upwind of the community of Babbitt.
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Figure 42. Air photo of the Babbitt, MN community PM sampling site with respect to the taconite mines and processing facilities.
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Figure 43a-b. Babbitt Municipal Building inactive local plant wind and precipitation composites.
Figure 44a-b. Babbitt Municipal Building active local plant wind and precipitation composites.
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Figure 45a-b. Babbitt Municipal Building winter season wind and precipitation composites.
Figure 46a-b. Babbitt Municipal Building summer season wind and precipitation composites.
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Table 35. TPSI calculation for Babbitt Municipal Building. Sample Season Activity Plant Mine PCF TPSI Series 331 W A 1 18 0 19 Series 351 W A 5 19 0 24 Series 371 W A 0 3 0 3 Series 531 W A 8 49 0 57 Series 551 W A 13 5 3 15 Series 641 W I 7 2 0 9 Series 671 W I 15 15 0 30 Series 701 S I 6 3 2 7 Series 741 S I 0 5 0 5 Series 771 S I 0 8 1 7 Series 831 S I 14 11 2 23 Series 851 S I 10 8 4 14 Series 921 S A 6 17 0 23 Series 951 S A 5 6 4 7 Series 1161 S A 11 4 2 13 Series 1301 S A 10 27 0 37 Where: TPSI = Taconite Particle Source Index (as a % of total sample time where wind is from potential sources). PCF = Precipitation Correction Factor (subtracted from “Plant” + “Mine” sources to derive TPSI).
Maximum Minimum Median Average Standard Deviation Winter Samples 57 3 19 22.4 16.4 Summer Samples 37 5 13 15.1 10.0 Inactive Samples 30 5 9 13.6 8.8 Active Samples 57 3 19 22.0 15.6
Maximum Minimum Median Average Standard Deviation Winter Inactive 30 9 19.5 19.5 10.5 Summer Inactive 57 3 19 23.6 18.1 Winter Active 23 5 7 11.2 6.6 Summer Active 37 7 18 20 11.4
During the winter sampling season, wind directions measured at the Babbitt community sampling site were primarily from the southwest, west, and northwest, with less common winds from the south and south-southeast (Fig. 45a). Winter season winds from northwest, west, and west-southwest were from directions absent of taconite processing plants and/or mines and associated mining infrastructure. Winds from the southwest, south, and southeast were from the direction of the Northshore taconite mine and associated infrastructure, and winds from the southeast would be from the direction of the Northshore primary crusher (Fig. 42). During the winter sampling season, winds greater than 1.8 m/s (4 miles per hour) were blowing approximately 78% of the time.
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Babbitt Municipal Building Taconite Particle Source Index (TPSI) 80 40
TPSI PM1
PM2.5 )] 70 3 PM10 MOUDI-T
60 30
50 [Weight / Volume Air (µg/m 40 20 TPSI (%)
30 , MOUDI-T 10
20 10 , PM 2.5 , PM 1 10 PM
0 0 Series 851 Series 951 Series 741 Series 831 Series 921 Series 701 Series 771 Series 671 Series 351 Series 531 Series 641 Series 331 Series 371 Series 551 Series 1301 Series 1161 Sample Series Events
Figure 47. Comparison of TPSI to PM concentrations by sample event at the Babbitt site.
During the summer sampling season, wind directions measured at the Babbitt community sampling site were primarily from west and west-southwest (Fig. 46a). Winds from the southwest, south, and southeast were less common (Fig. 46a). Predominant winds observed during summer sampling would be from a direction lacking taconite processing plants and/or taconite mines and associated mining infrastructure (west winds); however, the less common winds from the southwest, south, and southeast would be from directions where the Northshore mine and associated mining infrastructure occur. Southeast winds would also be from the direction of the Northshore primary crusher (Fig. 42). During the summer sampling season, winds greater than 1.8 m/s were blowing approximately 64% of the time (Table 31). Measurable precipitation occurred approximately 2.1% of the time during the winter season community sampling events in Babbitt (Fig. 45b). During summer season sampling events in Babbitt, measurable precipitation occurred approximately 7.4% of the time period during which air sampling occurred (Fig. 46b). During periods of time that air sampling took place at Babbitt while local taconite plants/mines were inactive, winds were primarily from the west and west-southwest, with winds less commonly blowing from the west-northwest, north, northeast and east directions (Fig. 43a). The winds directions measured during periods of taconite plant/mine inactivity at Babbitt would have from directions absent of taconite processing plants and local mines and associated mining infrastructure (Fig. 42).
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During sampling events when local taconite processing/mines were inactive, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants ranged from 0% to 15%, and the percentage of time that winds (> 1.8 m/s) were sourced from the directions of local mines and associated mining infrastructure ranged from 2% to 15% (Table 35). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were inactive was approximately 70% (Table 31). The overall percentage of time during which measurable precipitation was occurring regardless of wind speed for all community sampling events in Babbitt that were obtained while taconite processing plants/mines were inactive was less than 7.8% (Fig. 43b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from potential processing plant/mine sources (PCF) obtained when taconite processing plants/mines were inactive ranged from 0% to 4% (Table 35) for individual sampling series. During periods of time that air sampling that took place at Babbitt while local taconite plants/mines were active, winds were primarily from the west, with fewer occurrences of winds from the northwest, southwest, south, and south-southwest (Fig. 44a). The winds directions measured during periods of taconite plant/mine activity at Babbitt would have been primarily from the directions lacking local taconite processing plants and or local mine/mine-associated infrastructure; however, winds from the southwest to the southeast would have been from the direction of the Northshore open pit mine and associated mining infrastructure, and winds from the southeast would have been from the general direction of the Northshore primary crusher (Fig. 42). During sampling events when local taconite processing/mines were active, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants ranged from 0% to 13%, and the percentage of time that winds (> 1.8 m/s) were sourced from local mines and associated mining infrastructure ranged from 3% to 49% (Table 35). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were active was 71.1% (Table 31). The overall percentage of time during which measurable precipitation occurred during air sampling at Babbitt while taconite processing plants/mines were active was 2.9% (Fig. 44b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from a potential processing plant/mine source (PCF) that were obtained during air sampling at Babbitt when taconite processing plants/mines were active ranged from 0% to 4% (Table 35).
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Seasonal Comparisons The Babbitt Municipal Building was sampled a total of 16 times during the study (Table 17). This sampling included seven sampling events during the winter season and nine sampling events during the summer season between November 2008 and September 2009. The highest MOUDI total concentration recorded at the Babbitt site was 20.66 µg/m3 from sample series 331 (winter, active) and the lowest recorded was 6.69 µg/m3 from series 371 (winter, active) (Table 17). MOUDI totals for samples obtained from Babbitt during the winter season ranged from 6.69 µg/m3 to 20.66 µg/m3. MOUDI totals for samples obtained from Babbitt during the summer season ranged from 6.91 µg/m3 to 12.56 µg/m3 (Table 17). Figure 48a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for winter (7 samples) and summer (9 samples) collected at the Babbitt Municipal Building site. Error bars for each stage represent the standard deviation for the sample set for that particular size range (MOUDI) of PM. Statistical analysis comparing seasonal differences in mean PM concentrations of the Babbitt site show significant differences based on the season in which the samples were collected (Table 25). These significant differences are depicted by the graphs in Figure 48a-b. Although mean PM concentrations from the winter season (Fig. 48a) are dominated by a higher amount of finer particles (“accumulation” mode) ranging in size from 1.0 µm to less than 0.056 µm, the graph displays a distinct bimodal distribution of the PM. This differs significantly compared with the summer season PM concentrations from the Babbitt site (Fig. 48b) that vary little, resulting in a faint bimodal distribution curve. The average MOUDI total concentration for all samples collected in Babbitt was 10.41 µg/m3 (Tables 19–22), which is lower than the overall MOUDI total average for all samples from the five MIR communities (10.92 µg/m3; Tables 19 and 20). The average MOUDI total concentration for samples collected during the winter season at Babbitt is 11.97 µg/m3, which is lower than the average MOUDI total concentration for samples collected during the winter season from the five MIR communities (12.02 µg/m3; Tables 19 and 20). The average MOUDI total concentration for samples collected during the summer season at Babbitt was 9.19 µg/m3, which is lower than the average MOUDI total concentration collected during the summer season from the five MIR communities (10.09 µg/m3; Tables 19 and 20). 3 The average PM2.5 fraction (concentration) for the Babbitt site for all samples is 6.64 µg/m , which is higher than the average PM2.5 concentration for all samples collected from the five MIR communities 3 (6.61 µg/m ; Table 20). The average PM2.5 concentration for samples collected during winter season at 3 Babbitt was 8.08 µg/m , which is higher than the average PM2.5 concentration for samples collected 3 from the five MIR communities (7.31 µg/m ; Table 20). The average PM2.5 concentration for samples 3 collected during the summer season at Babbitt was 5.52 µg/m , which is lower than the average PM2.5 concentration for samples collected during the summer season from the five MIR communities (6.09 µg/m3; Table 20). The average PM2.5 percentage relative to the MOUDI total PM collected at Babbitt for all samples is 62.8%, which is higher than the average PM2.5 percentage collected from all samples from the five MIR communities (61.1%; Table 20). The average PM2.5 percentage for samples collected from Babbitt during the winter season was 67.6%, which is higher than the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (62.4%; Table 20). The average PM2.5 percentage for samples collected from Babbitt during the winter season was 59.1%, which is lower than the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (60.1%; Table 20).
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(a)
(b)
Figure 48a-b. Comparison of averaged MOUDI stages from Babbitt Municipal Building Site by winter season (7 samples) and summer season (9 samples). Bars = St. Dev.
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Local Mine/Plant Activity Seven samples were collected during inactive and nine samples were collected during active mine/plant operations near Babbitt (Table 17). MOUDI total concentrations obtained in Babbitt while local processing plants/mines were inactive ranged from 6.91 µg/m3 to 12.56 µg/m3. MOUDI total concentrations measured in Babbitt while local processing plants/mines were active ranged from 6.69 µg/m3 to 20.66 µg/m3 (Table 17). Figure 49a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988-2012) of PM for periods where local taconite processing plants/mines were inactive (7 samples) and for periods where local taconite processing plants/mines were active (9 samples) that were collected at the Babbitt sampling site. Both graphs display bimodal distribution with slightly higher concentrations of PM in the “coarse” mode (> PM1) during inactive plant/mine activity, as opposed to slightly higher concentrations of PM in the “accumulation” mode (< PM1) during active plant/mine activity. Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the differences in PM of the Babbitt Municipal Building site based on local plant/mine activity showed no significant differences (Table 28). The average MOUDI total concentration for all samples at Babbitt was 10.41 µg/m3 (Tables 19–22), which is lower than the average MOUDI total for all samples obtained from the five MIR communities (10.92 µg/m3; Tables 19–22). The average MOUDI total concentration for all samples collected at Babbitt during processing plant/mining inactivity was 9.59 µg/m3, which is lower than the average MOUDI total concentration for samples collected from the five MIR communities while processing plant/mining was inactive (10.31 µg/m3; Tables 21 and 22). The average MOUDI total concentration collected at Babbitt while processing plants/mines were active was 11.04 µg/m3, which is less than the average MOUDI total concentration for samples collected from the five MIR communities during processing plant/mining activity (11.52 µg/m3; Tables 21 and 22). 3 The average PM2.5 fraction (concentration) for all samples collected at Babbitt was 6.64 µg/m , which is higher than the average PM2.5 concentration for all samples collected from the five MIR 3 communities (6.61 µg/m ; Table 22). The average PM2.5 concentration for samples collected at Babbitt 3 during processing plant/mining inactivity was 5.63 µg/m , which is lower than the average PM2.5 concentration for samples collected during processing plant/mining inactivity in the five MIR 3 communities (6.39 µg/m ; Table 22). The average PM2.5 concentration for samples collected at Babbitt 3 during processing plant/mining activity was 7.42 µg/m , which is higher than the average PM2.5 concentration for samples collected from the five MIR communities during processing plant/mining activity (6.83 µg/m3; Table 22). The average PM2.5 percent fraction for all samples collected at Babbitt was 62.8%, which is lower than the average PM2.5 percent fraction for all samples collected from the five MIR communities (61.1%; Table 22). The average PM2.5 percent fraction for samples collected at Babbitt while processing plants/mining were inactive was 57.5%, which is lower than the average PM2.5 percent fraction for samples collected during processing plant/mining inactivity at the five MIR communities (62.1%; Table 22). The average PM2.5 percent fraction for samples collected at Babbitt while processing plant/mining was active was 67.0%, which is higher than the average PM2.5 percent fraction for samples collected during processing plant/mining activity from the five MIR communities (60.1%; Table 22).
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(a)
(b)
Figure 49a-b. Comparison of averaged MOUDI stages from Babbitt Municipal Building during local mine/plant Inactivity (7 samples) and Activity (9 samples). Bars = St. Dev.
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Silver Bay High School
Sample Site and Weather Conditions Even though Silver Bay is not technically located on the MIR, it was included with the other four MIR community locations (Keewatin, Hibbing, Virginia, and Babbitt) because of its close proximity to taconite processing activities. The rooftop community sample site in Silver Bay is located at the Silver Bay (Kelley) High School in the center of town between Banks Boulevard and Lake County Highway 15. The Northshore taconite plant is located east and south of the sample collection site between azimuths 81º and 167º and at a distance ranging from 0.5 to 1.0 mile. In the opposite direction, between azimuths 251º and 293º and at distances ranging from 3.5 to 4.0 miles, are Northshore’s taconite tailings basin, tailings (waste) piles, and associated haul roads (Fig. 50).
Weather Conditions Wind direction data obtained during sampling periods at the Silver Bay community sampling site are illustrated in Figures 51a-b (inactive plants), 52a-b (active plants), 53a-b (winter season) and 54a-b (summer season). Summary data for the weather conditions that existed during sampling at the Silver Bay community sampling location are found in Table 36, including the season, local plant activity, percentage of time winds were from the direction of the local taconite processing plant (Plant), percentage of time winds were from the direction of the local taconite mine(s) (Mine), the percentage of the sampling period during which precipitation was occurring (PCF), and the Taconite Particle Source Index (TPSI) calculated for each sampling series. An average ~30% TPSI was calculated for the 12 MIR community samples collected in Silver Bay, including four during the winter season (average winter TPSI equals 22.8%) and eight during the summer season (average summer TPSI equals 34.1%). The indices range from a low of 7% for sample series 651 (winter, inactive) to a high value of TPSI of 51% for sample series 911 (summer, active; Table 36). Due in part to Lake Superior’s moderated climate (cooler summer/warmer winter temperatures, wind direction, and precipitation changes (Phillips and McCulloch, 1972)), an eastern wind component can occur and influence the sample site in both seasons (an average slightly greater than 20% recorded during sample collection) and blows from the direction of Lake Superior. Measurable precipitation occurred during seven of the sampling series (Table 36). Despite predominant east winds from the direction of the Northshore taconite processing plant(especially during the summer season), statistical analyses comparing PM concentrations with TPSI indices show no statistically significant correlation of PM1, PM2.5, PM10, or MOUDI PM total concentration with the TPSI at the Silver Bay site (see statistical analyses, Table 30). A graphical portrayal of the data also illustrates the low correlations of PM concentrations to the TPSI (Fig. 55). 2 Statistical regressions comparing PM1, PM2.5, PM10, and MOUDI-T with the TPSI generate (R ) correlation values of 0.03, 0.04, 0.04, and 0.01, respectively. The regression p-values are the second highest of any of the MIR communities and confirm the lack of statistical significance between the TPSI and measured PM concentrations in the community.
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Figure 50. Air photo of the Silver Bay, MN community PM sampling site with respect to the taconite mines and processing facilities.
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Figure 51a-b. Silver Bay High School inactive local plant wind and precipitation composites.
Figure 52a-b. Silver Bay High School active local plant wind and precipitation composites.
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Figure 53a-b. Silver Bay High School winter season wind and precipitation composites.
Figure 54a-b. Silver Bay High School summer season wind and precipitation composites.
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Table 36. TPSI calculation for Silver Bay High School. Sample Season Activity Plant Basin PCF TPSI Series 651 W I 5 2 0 7 Series 661 W I 15 1 0 16 Series 691 S I 14 20 4 30 Series 731 S I 13 10 1 22 Series 751 S I 40 12 8 44 Series 821 S I 50 2 9 43 Series 841 S I 15 19 2 32 Series 911 S A 20 31 0 51 Series 941 S A 11 28 8 31 Series 1181 S A 15 7 2 20 Series 1661 W A 12 8 0 20 Series 1671 W A 48 0 0 48 Where: TPSI = Taconite Particle Source Index (as a % of total sample time where wind is from potential sources). PCF = Precipitation Correction Factor (subtracted from “Plant” + “Mine” sources to derive TPSI).
Maximum Minimum Median Average Standard Deviation Winter Samples 48 7 18 22.8 15.3 Summer Samples 51 20 31.5 34.1 10.2 Inactive Samples 44 7 30 27.7 12.7 Active Samples 51 20 31 34.0 13.3
Maximum Minimum Median Average Standard Deviation Winter Inactive 16 7 11.5 11.5 4.5 Summer Inactive 48 20 34 34.0 14.0 Winter Active 44 22 37.5 35.3 9.0 Summer Active 51 20 31 34 12.8
As previously mentioned, with respect to potential wind-carried PM and prevailing winds, the Silver Bay High School sampling site showed potential for the influence of PM from the processing plant to the east and the tailings basin to the west based on the examination of the seasonal wind rose diagrams (Figs. 53ab–54ab). The highest potential for mining-related PM occurs during the summer season, when winds are predominantly from two directions: 1) winds due west from the potential source of the tailings basin; and 2) winds from an easterly direction from Lake Superior and from the direction where the Northshore plant is located. Likewise, prevailing winds in summer and during plant activity are more east-northeast and east and are possibly just missing the high school sampling location. Prevailing winds during the winter season were from the north and northeast, from directions where no local taconite processing plant and/or mine infrastructure exists.
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Silver Bay High School Taconite Particle Source Index (TPSI) 80 40
TPSI PM1
PM2.5 )] 70 3 PM10 MOUDI-T
60 30
50 [Weight / Volume Air (µg/m 40 20 TPSI (%)
30 , MOUDI-T 10
20 10 , PM 2.5 , PM 1 10 PM
0 0 Series 821 Series 751 Series 941 Series 731 Series 911 Series 841 Series 661 Series 651 Series 691 Series 1181 Series 1671 Series 1661 Sample Series Events
Figure 55. Comparison of TPSI to PM concentrations by sample event at the Silver Bay site.
During the winter sampling season, wind directions measured at the Silver Bay community sampling site were primarily from the north, east-northeast and east, with less common winds from the north- northwest and northeast (Fig. 53a). Winter season winds from the north, east-northeast and east were from directions absent of taconite processing plants and/or mines and associated mining infrastructure (Fig. 50), as were winds from the north-northwest and northeast. Winds from the west-northwest to west-southwest, which made up a small percentage of the overall winds during winter season sampling at Silver Bay, were from the direction of the Northshore tailings basin and associated infrastructure. Winds from the southeast were from the general direction of the Northshore taconite processing plant (Fig. 50). During the winter sampling season, winds greater than 1.8 m/s (4 miles per hour) were blowing approximately 66% of the time. During the summer sampling season, wind directions measured at the Silver Bay community sampling site were nearly bimodal, with nearly equal percentages of the winds coming from easterly and westerly directions (Fig. 54a). Winds from the northeast were less common (Fig. 54a). Winds from the west would be from the direction of the Northshore tailings basin; winds from the east would be from the direction of the Northshore taconite processing plant (Fig. 50). During the summer sampling season, winds greater than 1.8 m/s were blowing approximately 60% of the time (Table 31).
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Measurable precipitation did not occur during winter season community sampling events in Silver Bay conducted for this study (Fig. 53b). During summer season sampling events in Silver Bay, measurable precipitation occurred 3.9% of the time period during which air sampling occurred (Fig. 54b). During periods of time that air sampling took place at Silver Bay while local taconite plants/mines were inactive, winds were primarily from the east and east-northeast, with winds less commonly blowing from the north, west, northeast, and north-northwest directions (Fig. 51a). Winds from the east were from the direction of the Northshore taconite processing plant; winds from the east-northeast were from directions absent of taconite processing plants and local mines and associated mining infrastructure (Fig. 50). During sampling events when local taconite processing/mines were inactive, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants ranged from 5% to 50%, and the percentage of time that winds (> 1.8 m/s) were sourced from the directions of the Northshore tailings basin and associated infrastructure ranged from 1% to 20% (Table 36). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were inactive was 61% (Table 31). The overall percentage of time during which measurable precipitation was occurring regardless of wind speed for all community sampling events in Silver Bay that were obtained while taconite processing plants/mines were inactive was approximately 2% (Fig. 51b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from potential processing plant/mine sources (PCF) obtained when taconite processing plants/mines were inactive ranged from 0% to 9% (Table 36) for individual sampling series. During periods of time that air sampling that took place at Silver Bay while local taconite plants/mines were active, winds were primarily from the east, west, and east-northeast (Fig. 52a). The winds directions measured during periods of taconite plant/mine activity at Silver Bay were primarily from the direction of the Northshore taconite processing plant (east and east-northeast winds); winds from the west were from the direction of the Northshore tailings basin and associated tailings basin infrastructure (Fig. 50). During sampling events when local taconite processing/mines were active, the percentage of time that winds (> 1.8 m/s) were sourced from the local taconite processing plants ranged from 11% to 48%, and the percentage of time that winds (> 1.8 m/s) were sourced from the Northshore tailings basin and associated infrastructure ranged from 1% to 20% (Table 36). The overall percentage of time that the wind was greater than 1.8 meters/second during periods when taconite processing plants/mines were active was 59.1% (Table 31). The overall percentage of time during which measurable precipitation occurred during air sampling at Silver Bay while taconite processing plants/mines were active was 2.3% (Fig. 52b). The percentage of time during which measurable precipitation was occurring when wind speeds were greater than 1.8 m/s from a potential processing plant/mine source (PCF) that were obtained during air sampling at Silver Bay when taconite processing plants/mines were active ranged from 0% to 8% (Table 36).
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Seasonal Comparisons Silver Bay High School was sampled a total of 12 times between April 2009 and April 2010. Four sampling events took place in the winter and eight sampling events took place during the summer season (Table 18). MOUDI totals ranged from a high of 23.05 µg/m3 in series 1181 (summer, active) to a low of 5.02 µg/m3 in series 691 (summer, inactive). Sample series 1181 was the highest recorded MOUDI total PM sample collected during this study (23.05 µg/m3). Figure 56a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for winter (4 samples) and summer (9 samples) collected at the Silver Bay High School site. Both graphs display clear bimodal distribution with higher concentrations of PM in the “coarse” mode (> PM1) during the winter season, and just slightly higher PM (> PM1) during the summer season. Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the seasonal differences in PM of the Silver Bay High School site showed no significant seasonal differences (Table 25). The average MOUDI total concentration for all samples collected in Silver Bay was 11.42 µg/m3 (Tables 19–22), which is higher than the overall MOUDI total average for all samples from the five MIR communities (10.92 µg/m3; Tables 19 and 20). The average MOUDI total concentration for samples collected during the winter season at Silver Bay is 13.05 µg/m3, which is higher than the average MOUDI total concentration for samples collected during the winter season from the five MIR communities (12.02 µg/m3; Tables 19 and 20). The average MOUDI total concentration for samples collected during the summer season at Silver Bay was 10.60 µg/m3, which is higher than the average MOUDI total concentration collected during the summer season from the five MIR communities (10.09 µg/m3; Tables 19 and 20). 3 The average PM2.5 fraction (concentration) for the Silver Bay site for all samples is 6.37 µg/m , which is lower than the average PM2.5 concentration for all samples collected from the five MIR communities 3 (6.61 µg/m ; Table 20). The average PM2.5 concentration for samples collected during winter season at 3 Silver Bay was 6.59 µg/m , which is lower than the average PM2.5 concentration for samples collected 3 from the five MIR communities (7.31 µg/m ; Table 20). The average PM2.5 concentration for samples 3 collected during the summer season at Silver Bay was 6.25 µg/m , which is lower than the average PM2.5 concentration for samples collected during the summer season from the five MIR communities (6.09 µg/m3; Table 20). The average PM2.5 percentage relative to the MOUDI total PM collected at Silver Bay for all samples is 56.5%, which is lower than the average PM2.5 percentage collected from all samples from the five MIR communities (61.1%; Table 20). The average PM2.5 percentage for samples collected from Silver Bay during the winter season was 51.5%, which is lower than the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (62.4%; Table 20). The average PM2.5 percentage for samples collected from Silver Bay during the winter season was 59.0%, which is lower than the average PM2.5 percentage for samples collected during the winter season from the five MIR communities (60.1%; Table 20).
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(a)
(b)
Figure 56a-b. Comparison of averaged MOUDI stages from Silver Bay High School Site by winter season (4 samples) and summer season (9 samples). Bars = St. Dev.
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Local Mine/Plant Activity Of the nine samples collected at Silver Bay, seven were collected during periods where the local taconite processing facility was inactive, and five were collected during periods where the local taconite facility was active. MOUDI total concentrations obtained in Silver Bay while local processing plants/mines were inactive ranged from 5.02 µg/m3 to 15.84 µg/m3. MOUDI total concentrations measured in Silver Bay while local processing plants/mines were active ranged from 8.12 µg/m3 to 23.05 µg/m3 (Table 18). Figure 57a-b displays average size distribution plots (generated using DistFITTM2009.01; Chimera Technologies, Inc., 1988–2012) of PM for periods where local taconite processing plants/mines were inactive (7 samples) and for periods where local taconite plants/mines were active (5 samples) that were collected at the Silver Bay sampling site. Both graphs display clear bimodal distribution with higher concentrations of PM in the “coarse” mode (> PM1). Error bars for each stage represent the standard deviation for the sample set for that particular size range of PM. Statistical analysis of the differences in PM of the Silver Bay High School site based on local plant/mine activity showed no significant differences (Table 25). The average MOUDI total concentration for all samples at Silver Bay was 11.42 µg/m3 (Tables 19– 22), which is higher than the average MOUDI total for all samples obtained from the five MIR communities (10.92 µg/m3; Tables 19–22). The average MOUDI total concentration for all samples collected at Silver Bay during processing plant/mining inactivity was 9.94µg/m3, which is lower than the average MOUDI total concentration for samples collected from the five MIR communities while processing plant/mining was inactive (10.31 µg/m3; Tables 21 and 22). The average MOUDI total concentration collected at Silver Bay while processing plants/mines were active was 13.49 µg/m3, which is higher than the average MOUDI total concentration for samples collected from the five MIR communities during processing plant/mining activity (11.52 µg/m3; Tables 21 and 22). 3 The average PM2.5 fraction (concentration) for all samples collected at Silver Bay was 6.37 µg/m , which is lower than the average PM2.5 concentration for all samples collected from the five MIR 3 communities (6.61 µg/m ; Table 22). The average PM2.5 concentration for samples collected at Silver Bay 3 during processing plant/mining inactivity was 5.78 µg/m , which is lower than the average PM2.5 concentration for samples collected during processing plant/mining inactivity in the five MIR 3 communities (6.39 µg/m ; Table 22). The average PM2.5 concentration for samples collected at Silver Bay 3 during processing plant/mining activity was 7.18 µg/m , which is higher than the average PM2.5 concentration for samples collected from the five MIR communities during processing plant/mining activity (6.83µg/m3; Table 22). The average PM2.5 percent fraction for all samples collected at Silver Bay was 56.5%, which is lower than the average PM2.5 percent fraction for all samples collected from the five MIR communities (61.1%; Table 22). The average PM2.5 percent fraction for samples collected at Silver Bay while processing plants/mining were inactive was 58.5%, which is lower than the average PM2.5 percent fraction for samples collected during processing plant/mining inactivity at the five MIR communities (62.1%; Table 22). The average PM2.5 percent fraction for samples collected at Silver Bay while processing plant/mining was active was 53.6%, which is lower than the average PM2.5 percent fraction for samples collected during processing plant/mining activity from the five MIR communities (60.1%; Table 22).
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(a)
(b)
Figure 57a-b. Comparison of averaged MOUDI stages from Silver Bay High School during local mine/plant Inactivity (7 samples) and Activity (5 samples). Bars = St. Dev.
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INFLUENCES OF PLANT ACTIVITY DISCUSSION The six taconite processing plants in northeastern Minnesota experienced various time periods encompassing either partial or full shutdowns as a result of the low demand for steel during the great recession. Table 37 lists an approximate compilation of MIR taconite processing plant closures/slow- downs during this period. For the purposes of comparing PM during inactive and active plant/mine operation, this community sampling study included plant shutdown periods of both full and partial plant shutdowns. In comparison, the plant sampling study only looked at and compared fully shut down plants (inactive) with actively operating plants. The NRRI was able to sample three of the six taconite plants during full shut down mode (Keetac, Hibtac, and Northshore). Further details can be found in the Taconite Plant Gravimetric Report (Monson Geerts et al., 2018b).This interruption in production allowed NRRI scientists the opportunity to collect aerosol PM samples in both the shut-down plants and in the surrounding communities while the plants were shut down. This presented the NRRI with the best possible opportunity to sample aerosol PM under conditions in which the inputs of PM from the taconite processing plants and mines were minimized. Such conditions represent the best opportunities to obtain background (no taconite processing/mining activities) conditions in the MIR communities with nearby mining/processing operations. Of the total 78 community PM samples collected, 54 of the samples were collected from communities located within the Mesabi Iron Range. The other 24 samples were collected from the three community background sites (Ely, Duluth, and Minneapolis). The 54 community samples are evenly split into 27 PM samples from communities where at least one local plant was active and 27 samples from the same communities that were collected when all of the local plants were shut down or partially shut down (inactive). In the case of the community of Babbitt, MN, even though the majority of Cliffs Natural Resources taconite processing facility is located in Silver Bay, MN, the primary crushing facility, as well as the mine pits, waste rock piles, mine roads, etc., are located at their Peter Mitchell Mine within ~3.5 miles of town and are thus potential mineral PM sources for that community. The average of MOUDI total PM concentrations from each of the two data sets reveal an overall average of 11.52 µg/m3 for communities sampled during active processing plants (n=27) compared with 10.31 µg/m3 for locations sampled during inactive plants (n=27) (Tables 21–22). Although these data equate to an increase in average total PM concentration of ~12% during plant activity versus plant inactivity, the statistical analyses of the data show no significant differences (Table 22). The average 3 PM2.5 fraction concentrations were found to be 6.83 µg/m in the communities while plants were active. The average PM2.5 fraction obtained in the communities during periods of plant inactivity was 6.39 µg/m3. This same relationship was also examined using the PM2.5 fraction from each of the MIR communities, resulting in an overall average 6.83 µg/m3 during active compared with 6.39 µg/m3 during inactive mines and processing plants (Table 22). Once again, the statistical analyses show that there is no significant difference due to plant/mine activity, not only with PM2.5 but also PM10 and PM1. Comparisons between individual samples, as well as between averages from each of the five MIR communities, are depicted in Figures 58–61. Figure 62 combines the MOUDI total PM concentration averages and PM2.5 concentration averages from each of the eight community locations and plots them relative to the NAAQS standards. MIR 3 community averages PM2.5 concentrations were consistently below the NAAQS PM2.5 limit of 12 µg/m . The average MOUDI total PM concentrations, which are higher than the PM10 fraction, are at 3 concentrations below the NAAQS PM10 limit of 35 µg/m .
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Table 37. Timeline of Mesabi Iron Range taconite processing plant closures.
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Comparison of All Community Samples by Local Plant Inactivity versus Activity - MOUDI Totals - Weight / Volume Air (µg/m3) 25
20 ) 3
15
10 Concentration - Weight / Volume Air (µg/m
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0 Babbitt Active 551 Babbitt Active 951 Babbitt Active 331 Virginia Active 991 Virginia Active 311 Babbitt Active 921 Babbitt Active 371 Babbitt Active 531 Virginia Active 471 Virginia Active 501 Virginia Active 621 Babbitt Active 351 Hibbing Active 721 Hibbing Active 451 Virginia Active 571 Hibbing Active 711 Hibbing Active 681 Hibbing Active 631 Hibbing Active 521 Babbitt Active 1161 Babbitt Active 1301 Babbitt Inactive 771 Babbitt Inactive 701 Babbitt Inactive 741 Babbitt Inactive 671 Babbitt Inactive 641 Virginia Inactive 961 Babbitt Inactive 851 Babbitt Inactive 831 Virginia Inactive 811 Virginia Inactive 801 Virginia Inactive 931 Hibbing Inactive 781 Hibbing Inactive 971 Silver Bay Active 941 Silver Bay Active 911 Keewatin Active 2201 Hibbing Inactive 1001 Keewatin Inactive 981 Keewatin Inactive 421 Keewatin Inactive 441 Keewatin Inactive 511 Keewatin Inactive 791 Silver Bay Active 1671 Silver Bay Active 1181 Silver Bay Inactive 661 Silver Bay Inactive 751 Silver Bay Active 1661 Silver Bay Inactive 841 Silver Bay Inactive 731 Silver Bay Inactive 691 Silver Bay Inactive 821 Silver Bay Inactive 651 Keewatin Inactive 1011
Figure 58. Comparison of all community samples by local plant inactivity versus activity – MOUDI totals (weight/volume air – µg/m3).
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Comparison of All Community Samples by Plant Inactivity versus Activity - PM2.5 Fraction - Weight / Volume Air (µg/m3) 25
20 ) 3
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10 Concentration - Weight / Volume Air (µg/m
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0 Babbitt Active 531 Babbitt Active 951 Virginia Active 991 Virginia Active 311 Babbitt Active 921 Babbitt Active 371 Babbitt Active 331 Babbitt Active 351 Babbitt Active 551 Hibbing Active 451 Hibbing Active 711 Virginia Active 621 Virginia Active 571 Virginia Active 501 Virginia Active 471 Hibbing Active 721 Hibbing Active 681 Hibbing Active 631 Hibbing Active 521 Babbitt Active 1301 Babbitt Inactive 671 Babbitt Inactive 771 Babbitt Active 1161 Babbitt Inactive 701 Babbitt Inactive 851 Babbitt Inactive 741 Babbitt Inactive 831 Babbitt Inactive 641 Virginia Inactive 961 Virginia Inactive 931 Virginia Inactive 811 Virginia Inactive 801 Hibbing Inactive 781 Hibbing Inactive 971 Silver Bay Active 911 Silver Bay Active 941 Hibbing Inactive 1001 Keewatin Inactive 441 Keewatin Active 2201 Keewatin Inactive 421 Keewatin Inactive 791 Keewatin Inactive 511 Keewatin Inactive 981 Silver Bay Active 1671 Silver Bay Active 1181 Silver Bay Active 1661 Silver Bay Inactive 661 Silver Bay Inactive 751 Silver Bay Inactive 841 Silver Bay Inactive 691 Silver Bay Inactive 731 Silver Bay Inactive 821 Silver Bay Inactive 651 Keewatin Inactive 1011
Figure 59. Comparison of all community samples by local plant activity – PM2.5 (respirable) fraction of MOUDI totals (weight/volume air – µg/m3).
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Comparison of Community Average Concentrations by Plant Activity - MOUDI Totals [Weight / Volume Air (µg/m3)] 25
20 ) 3 Virginia City Hall
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10 Concentration - Weight / Volume Air (µg/m
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0 Babbitt Active, n=9 Hibbing Active, n=6 Virginia Active, n=6 Babbitt Inactive, n=7 Keewatin Active, n=1 Virginia Inactive, n=4 Hibbing Inactive, n=3 Silver Bay Active, n=5 Keewatin Inactive, n=6 Silver Bay Inactive, n=7
Figure 60. Comparison of community concentration averages during plant inactivity versus activity – MOUDI totals [weight/volume air (µg/m3)].
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Comparison of Community Average Concentrations by Plant Activity - PM2.5 [Weight / Volume Air (µg/m3)] 25
20 ) 3 Virginia City Hall
15
10 Concentration - Weight / Volume Air (µg/m
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0 Babbitt Active, n=9 Virginia Active, n=6 Hibbing Active, n=6 Babbitt Inactive, n=7 Keewatin Active, n=1 Virginia Inactive, n=4 Hibbing Inactive, n=3 Silver Bay Active, n=5 Keewatin Inactive, n=6 Silver Bay Inactive, n=7
Figure 61. Comparison of community concentration averages during plant inactivity versus activity – PM2.5 fraction (weight/volume air – µg/m3).
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TOTAL AVERAGED PARTICULATE MATTER IN THE AIR 25 LOCAL LOCAL ) 3 BACKGROUND PLANT PLANT INACTIVE ACTIVE 20
TOTAL NAAQS PM STANDARD 2.5 PM 2.5 15
10
5 Averaged Particulate Matter Concentrations (µg / m
0
Ely, n=6 ng, n=3
MPLS, n=6 Duluth, n=8 Babbitt, n=9 Hibbi Virginia, n=5Babbitt, n=7 Hibbing, n=6Virginia, n=5 Keewatin, n=4 Keewatin, n=1 Silver Bay, n=7 Silver Bay, n=6
3 Figure 62. Comparison of inactive and active concentration averages by location – Total and PM2.5 (weight/volume air – µg/m ).
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The exact contribution of active local taconite processing facilities on mineral PM in the surrounding communities is complex. As previously mentioned, these complexities can include the exact definition of plant closure and whether or not the plant is totally shutdown or certain aspects of the plant are still running. It also can include seasonal variations between winter and summer season collection and all of the meteorological variables (i.e., prevailing winds, humidity, precipitation, etc.) that go with each (see wind and precipitation rose diagrams). When analyzed by the season in which the samples (MOUDI totals) were collected, MIR communities averaged slightly more than 19% greater PM levels during the winter season (12.02 µg/m3) versus the summer season (10.09 µg/m3) (Tables 19 and 20). The Babbitt site was the only MIR location that showed statistically significant higher PM concentrations in the winter season versus the summer season. This seasonal effect could be a function of the sample population, since the active data set includes approximately 45% more winter season (16) samples than summer season (11) samples. Likewise, the inactive sample set may be biased by the inclusion of 7 winter season samples relative to 20 summer season samples. However, the difference may also be attributable to one or more factors other than potential sample population effects (e.g., increased amount of heating with wood during winter months; (Marple, personal comm.)). Although slight differences were observed between the two data sets representing MIR community PM sampling during both active and inactive taconite plants/mines operations, none of the communities showed statistically significant higher PM concentrations during active versus inactive local taconite plants/mines. In the end, because so many variables exist, it is difficult to quantify the relationship and significance between mining and local community ambient PM concentrations; therefore, caution should be exercised when characterizing community air quality.
SIZE FRACTIONATED PARTICULATE MATTER - REPRESENTATIVE GRAPHS The MOUDI cascade impactor is able to size-fractionate particulate matter by aerodynamic diameter (Marple et al., 2014). This instrument collects various sizes of PM on individual sampling stages. Once the weight of PM has been normalized using the air volume in which the particles were collected, the stage masses can then be compared in terms of concentrations (µg/m3, for example). In general, the graphing of PM mass concentrations (weight/volume air) by aerodynamic diameter, from a single sample on a lognormal scale, results in a unique bimodal pattern. In ambient air PM fractionated samples collected by the MOUDI II sampler used in this study, the “coarse” mode particles, ranging in size from 18 µm down to 1.0 µm, make up the first mode (right side of a plot). These particles are primarily composed of particles (i.e., minerals) generated by comminution (e.g., crushing or grinding). Finer particles, ranging in size from 1.0 µm to less than 0.056 µm, form a second “accumulation” mode (left side of a plot). These particles are typically composed of particles generated through chemical reactions, such as combustion (Hinds, 1999). The primary objective of this study was to characterize the mineral PM from the communities and plants on the MIR. An important component of this characterization involves the examination of particle distribution by concentration and size. A series of graphs representing the averages from each of the three background sites (seasonal) (Figs. 11ab, 14ab, 17ab) and five MIR community sites (both seasonal and plant activity) (Figs. 24ab, 25ab, 32ab, 33ab, 40ab, 41ab, 48ab, 49ab, 56ab, and 57ab were generated using the computer software DistFit™ 2009.01 (Chimera Technologies, Inc., 1988–2012). In most of the locations, the bimodal characteristic of the aerosol PM is apparent. Graphs from the five MIR communities display average MOUDI stage concentrations for samples collected during inactive and active local mines/plants. Each graph includes a curve-fitting function, which highlights the separate modes. Error bars for each stage represent the standard deviation for the sample set. Graphs for the background locations are set up in the same manner; however, because there are no local mines/plants, the groupings are by season. Background graphs were also generated to emphasize the bimodal nature of the PM as well as to illustrate differences between seasons.
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Particulate Matter Mode Comparisons Comparisons of the PM modes from aerosol samples in MIR communities may also indicate the influences of mineral PM from potential mining/processing sources. The aerosol measurements from the communities and background locations are primarily bimodal in their size distribution. Ambient air samples from community locations, where comparisons between active versus inactive mines/plants are dominated by larger coarse PM modes, may indicate influence of mining activities. While not an exclusive indicator of PM contribution by mining activities, these graphs offer visual comparisons relative to: 1) PM mode differences; 2) differences compared with background locations; 3) differences between active and inactive mine/plants; and 4) differences between seasonal sample collections. Therefore, the graphs provide additional characterization and visual support for the statistical analyses of the PM data from the MIR communities. Tables 38 and 39 show the average PM mode concentrations and their percent of the (MOUDI) total, by community sample location, with respect to mine/plant activity and season in which the samples were collected, respectively. Statistical analysis of the data (located previously in the Data Interpretation section of this report) showed there were no significant differences between overall MIR communities’ modal PM concentration averages compared with the Ely background site (Tables 26 and 27). However, comparison of the percent PM showed that a higher coarse mode and lower PM1 mode were significant between MIR communities and the Ely background site, but only when the local mines/plants were active. These data would seemingly indicate at least some contribution to the MIR communities from mining practices. Slight increases in modal concentrations and percent PM were detected in some of the MIR communities when individually comparing the PM modes based on the local mines’/plants’ activities. However, these differences were found to be insignificant, with no correlation (Table 28).
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Table 38. Average concentrations by “Coarse” and “Accumulation” (PM1) modes – MIR community samples by local mine/plant activity: weight/volume air (µg/m3) and percent (%) with (standard deviation).
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Table 39. Average concentrations by “Coarse” and “Accumulation” (PM1) modes – MIR communities and background sites by season in which samples were collected: weight/volume air (µg/m3) and percent (%) with (standard deviation).
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PM Modes Based on Plant Activity Inactive Plants Comparing the separate modes from MIR communities for just the inactive plant data shows only one location in which the modes vary dramatically. At the Keewatin site, the coarse mode averaged 3.51 3 3 µg/m (37%) compared with 5.98 µg/m (63%) for PM1 (Fig. 25ab; Table 32). Although Keewatin’s PM1 basically equals the overall average (5.32 µg/m3) from the MIR communities, its coarse mode is substantially less than the overall average (4.99 µg/m3). Because Keetac was inactive for the longest period of time (about 13 months) compared to the other taconite facilities, the Keewatin community site was removed from the statistical analysis, as only one sample could be collected while the plant was active. Because the difference in modes is so great, it may be related to Keewatin’s far western location on the MIR, which effectively renders it immune from the possible accumulation effects of PM generated by any mines/plants to the west and delivered through prevailing winds (Figs.19-22). However, because no statistical analyses were conducted on Keewatin samples based on plant activity, any conclusions that follow are merely speculative. Mode comparisons from inactive plants for the remaining four MIR communities were very similar and also support the statistical analysis (Table 28).
Supplementary Active Plants Comparing the separate modes from MIR communities for just the active plant data shows a slight increase in the coarse mode at Hibbing, Virginia, and Silver Bay (Figs. 33, 41, and 57; Table 38). In evaluating the separate modes from the active data, three locations show modes that have this trend. Two of these locations—Virginia and Silver Bay—show substantially higher coarse modes (> 7.15 µg/m3, 3 > 57%) than PM1 (> 5.27 µg/m , > 42%), which may indicate influences from mining sources. However, statistical analysis found no significant difference between modes based on plant activity (see statistical analysis, Table 28). Additionally, the Babbitt site data shows the opposite trend, with substantially higher concentrations of PM1 versus coarse mode. Although this difference was also insignificant, Babbitt’s PM distributions more closely resemble the overall average concentrations from community samples collected when mines/plants were inactive. This phenomenon may have to do with the town’s location (only site north of the Laurentian Divide) that possibly shields the community from PM carried by prevailing winds (Figs. 45–46 in much the same way as in Keewatin.
PM Modes Based on Seasonal Differences With regard to seasonal variations, higher average concentrations of PM were present in both modes in the MIR communities during the winter versus the summer season. Overall, average 3 3 3 concentrations for coarse mode PM were 5.90 µg/m and 5.08 µg/m ; PM1 were 6.12 µg/m and 5.01 3 µg/m for winter and summer, respectively (Table 39). Only the PM1 average concentration was found to be statistically significant (Table 24). Higher levels of PM1 compared with the coarse mode, in the winter in northeastern Minnesota, may also reflect the effects of wood burning as a heating source (Marple, personal comm.). On an individual basis, the communities of Virginia and Silver Bay were the only two communities where average concentrations were greater in the coarse mode compared to PM1, for both seasons. The average PM1 concentration at Babbitt in the winter was significantly greater than in the summer (Table 25). The percent fraction of the total for average PM1 at Babbitt also shows this. Conversely, the percent fraction of the total for average coarse mode at Babbitt shows the opposite, where summer was significantly greater than winter (Table 25). Babbitt was the only MIR community that showed any significance with respect to PM modes. Differences in the three background sites—one rural site north of the MIR versus two urban sites south of the MIR—had some interesting aspects. On an individual basis, the background site of Ely tended to follow the same trend as the MIR communities, with higher average winter PM
NRRI/RI-2019/30 – Community Gravimetric Analysis 144 concentrations, whereas Duluth and Minneapolis had higher average PM concentrations in both modes during the summer season. The higher PM1 mode in the urban background sites are more than likely due to greater amounts of exhaust from sources of combustion (Marple, personal comm.). However, the average concentration of coarse mode in Duluth during the summer exceeded that of the PM1, which may be the result of operating gravel pits to the west of the NRRI site during the summer season only. The average concentration of coarse mode during the summer at Duluth is significantly greater than in the winter. Likewise, the percent fraction of the total for average PM1 and coarse mode at Duluth are also statistically significant (Table 25). Duluth is the only background site that showed any significance with respect to PM modes.
Graph Comparisons Whether comparing the MIR communities by the amount of PM with regard to the activity of a local mine/plant or a background site by the season in which the sample was collected, the graphs of the mineral PM data are not substantially different (Figs. 25ab, 33ab, 41ab, 49ab, and 57ab). Subtle differences in the graphs may represent variations in geographical localities, direction and proximity to potential sources, and/or varying meteorological conditions. Thus, characterization of the mineral PM in this study was accomplished by utilizing multiple samples and averaging the concentrations. In general, with the exception of the Keewatin site, due to insufficient sample collection during active mine/plant operations, examination of the sets of graphs from each of the MIR communities shows little if any difference in PM concentrations between inactive and active mine/plants. This conclusion is supported by the results of the statistical analyses (see statistical analysis, Table 28). Compared with the background sites (Figs. 11ab, 14ab, and 17ab), differences are evident between seasonal modes in Ely and Duluth. However, the differences at Ely are not great enough to be statistically significant (Table 25). Conversely, the coarse mode PM concentrations in Duluth are significantly greater in summer than in winter. Also, the percent fraction of PM1, PM2.5, and PM10 of the total PM are significantly greater in the winter than in summer (Table 25). Seasonal modal comparisons for the Minneapolis background site show similar concentrations and vary little, also supporting the statistical analyses.
IN SUMMARY It is important to state that the NRRI’s community aerosol particulate matter (PM) sampling and characterization protocol was not meant to represent—or be considered a substitute for—ambient air sampling as conducted and reported by regulatory agencies in the state of Minnesota. Because NRRI did not conduct an exposure study, and therefore did not conduct exposure study sampling, resultant data are not intended to be used for purposes of calculating risk assessment. References in this report to EPA, NAAQS, OSHA, and MSHA standards are for illustrative and comparative purposes. Nevertheless, the NAAQS PM10 and PM2.5 standards remain established and recognized quantitative air quality benchmarks and, therefore, provide a logical frame of reference and context for the reporting of the study’s finding. While the MOUDI II impactors used by NRRI for collecting the ambient community air samples differ from the high-volume samplers typically used by regulatory agencies such as MPCA and EPA, the study’s community air sampling results have been shown to be in good agreement with PM2.5 and PM10 levels throughout Minnesota that have been obtained by ongoing MPCA regulatory air monitoring. The same MOUDI II aerosol sampling instruments were utilized for NRRI’s community sampling and in-plant sampling (a MOUDI II was also used by the University of Minnesota SPH during its occupational exposure study; Hwang et al., 2013; Hwang et al., 2014). Utilization of the same type of instrumentation by both NRRI and University of Minnesota SPH studies maintains a critically important level of consistency for comparing and evaluating the Minnesota Taconite Worker Health Study results in their entirety.
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The study’s choice of fixed rooftop sampling locations instead of ground-level sites within the communities was based on security, practicality (e.g., access to power), and the ability to concurrently collect meaningful meteorological data. Community/public building rooftops are often used by regulatory agencies as secure sites for conducting air sampling programs and for recording meteorological data (Winberry, 1999). The rooftop locations also provided a sampling environment that was more immune from localized ground-level disturbances that could have contributed episodic quantities of PM that would have had the effect of “contaminating” and inordinately skewing the five- to seven-day ambient air sampling results. The PM source(s) of interest (mines and/or processing facilities) were typically located two to eight kilometers from the communities. Therefore, locating the MOUDI impactors on rooftops 10 or more meters above the ground was a scientifically justifiable practice consistent with EPA community sampling recommendations (Winberry, 1999) as well as consistent with the study’s ambient air characterization objective.
CONCLUSIONS Gravimetric characterization of the aerosol PM within communities located on the Mesabi Iron Range in northeastern Minnesota included a total of 54 separate PM sampling events between November 2008 and September 2010. An additional 24 sampling events were conducted at background locations. All eight sites (five MIR communities and three background sites) were sampled at least three times during both summer season (May through October) and winter season (November through April). Each of the sampling events consisted of scheduled 120- to 168-hour (5- to 7-day) sample collections using the 120 MOUDI II cascade impactor and total filter sampler. The resulting gravimetric data was normalized into concentrations using the volume of air sampled 3 as weight/volume air (µg/m ). Particulate matter was divided into PM1, PM2.5 (respirable), PM10, and (MOUDI) total PM. The characterization of the PM from each location was done primarily by the season in which the samples were collected and the activity of local taconite mines/plants (five MIR locations only). Further comparisons of the data included: 1) using the Taconite Particle Source Index (TPSI); and 2) assessing coarse PM (≥ 2.5µm ≤ 10µm) with that of PM1 (< 1.0 µm). The TPSI is a number assigned to each MIR community sample calculated from meteorological data collected at the time of sampling. The index largely represents the percent time that winds greater than 1.8 meters/second (~4 mph) are blowing from a potential source. Potential sources include the mines (including: pits, haul roads, and active waste rock piles) and local taconite processing facilities/plants and associated tailings basins. The equipment and methods of sample collection used by the NRRI to characterize PM in the five MIR communities, including the 120 MOUDI II cascade impactor, were in good agreement and consistent throughout the sample collection period (Marple et al., 2014). Statistical analysis indicates that NRRI PM2.5 and PM10 from the Virginia site data (2009) showed no significant difference compared with those determined by state regulatory sampling (MPCA, 2010) using EPA-accepted equipment.
Findings . Study conclusions find that all MIR community samples have concentration less than the NAAQS limits for PM10 and PM2.5 (Please keep in mind that the NRRI's community air sampling methodology and reported PM2.5 (and PM10) data are not meant to be considered a substitute for ambient air sampling as conducted and reported by regulatory agencies such as MPCA and EPA. NRRI has referenced the NAAQS PM2.5 standard for illustrative and comparative purposes and to provide context to its community (and background location) air sampling findings, because the NAAQS PM2.5 standard is an established and accepted air quality benchmark.). . An index, called the “Taconite Particle Source Index” (TPSI), was assigned to each sample with the intention of correlating PM concentrations with meteorological data collected at the time of sampling. The index largely represents the percent time that winds greater than
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1.8 meters/second (~4 mph) were blowing from a potential source of mining-related PM (including: mine pits, haul roads, tailings basins, and active waste rock piles) and local taconite processing facilities/plants. Significant correlation between PM and TPSI was found in the communities of Virginia (negative) and Babbitt (positive). There was no correlation between the TPSI and PM in the other three MIR community locations. . Individually, for most communities except Babbitt and Duluth there was no significant seasonal difference in PM. In Babbitt, PM1 and PM2.5 concentrations and proportions tended to be significantly greater in winter. In Duluth, the major seasonal difference was shown in the proportions of different particle sizes. In winter, there were significantly more fine particles (PM10 and less) and less coarse particles (≥ PM2.5 ≤ PM10) than in the summer. . Statistical analysis concluded that there was no significant difference in mean PM concentration levels at the five MIR community locations when local mine/plants were active compared to when they were inactive. Similarly, there was no significant difference identified for PM concentrations between MIR communities and the Ely background location. . The PM concentrations and proportions across the MIR were consistent and did not display any differences with respect to changes in the geology of the iron-formation due to metamorphism. . Statistical analysis concluded that there was no significant difference between overall MIR community PM concentration averages compared with the Ely background site. However, higher coarse mode and smaller PM1 mode percentages were significant between MIR communities and the Ely background site, but only when the local mines/plants were active.
Further work Upon conclusion of the Minnesota Taconite Workers Health Study, no associated follow-up studies are currently planned with regard to the monitoring of PM levels in the MIR community or background sites.
ACKNOWLEDGEMENTS The Minnesota Legislature is gratefully acknowledged for providing base funding for the Minnesota Taconite Workers Health Study (MTWHS), as are the Iron Range Legislative Delegation for their efforts and advocacy for securing that funding. The Natural Resources Research Institute (NRRI) is also acknowledged for providing significant supplemental project support via the Permanent University Trust Fund (PUTF). The NRRI would also like to thank our colleagues at the University of Minnesota School of Public Health (SPH) – in particular, study leaders Drs. John Finnegan and Jeffrey Mandel. As our SPH colleagues have stated, this undertaking was the result of the concerted effort of the entire Lung Health Partnership, and contributors to this effort were many. The NRRI Particle and Material Characterization Group would like to thank the following industry representatives for their time and patience, and also for the safe access within the taconite processing facilities: Mr. Kelly R. (Rob) Campbell – Industrial Hygiene Specialist/Cliffs Natural Resources, for access to Northshore and Utac; Ms. Karla L. Heritage-McKenzie – Safety Manager/ArcelorMittal, for access to Minorca; Mr. Kent Swanson – Staff Supervisor/Safety & I.H./U.S. Steel, for access to Minntac and Keetac; and Ms. Stephanie Bigelow – Safety Representative (along with Rob Campbell), for access to Hibtac. The NRRI’s Particle Study project team extends additional thanks to several individuals for their contributions and input, starting with Anda Bellamy, editor and publications specialist. Anda’s editing, organizing, and assembly of the team’s final reports was a huge task. Next is Tamara Diedrich, who initiated and oversaw many key components of the NRRI’s early project work. We also wish to thank the members of the NRRI Particle Study Science Advisory Board (SAB), composed of D. Wayne Berman (AEOLUS Inc.), Gregory Meeker (United States Geological Survey – USGS), Paul Middendorf (National
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Institute of Occupational Safety and Health – NIOSH), and Daniel Vallero (U.S. Environmental Protection Agency – USEPA) who provided guidance, recommendations, and constructive criticism during the course of this work; their collective inputs were of significant assistance to the NRRI team, and their advisory role was much appreciated. A deep expression of gratitude is given to Professor Emeriti Dale Lundgren (University of Florida) and the late Virgil Marple (University of Minnesota), as well as Bernard Olson (University of Minnesota), Bryan Bandli (University of Minnesota Duluth), and Francisco Romay (MSP Corporation – MOUDI), for the key roles they played advising the technical aspects of our aerosol science-based experimental designs, sampling, and particulate matter (PM) analysis and characterization. Special thanks are also extended to former NRRI team members Devon Brecke and Megan Schreiber, who played important sample collection and laboratory support roles, and to the NRRI’s Meijun Cai for her statistical review and analysis of the project’s community, background, and taconite facility datasets. We would also like to thank the dedication and hard work of all the student workers who contributed to this effort over the years, including: Alanna Schwanke, Chris Bicknese, April Severson, Allison Severson, Stuart Kramer, and Matt Chaffee. Minnesota agencies are also thanked for providing feedback to the NRRI’s work. They include the MPCA, Minnesota Department of Health (MDH), Minnesota Department of Natural Resources (MDNR), and the Department of Iron Range Resources & Rehabilitation (DIRRR). Lastly, the NRRI investigators wish to acknowledge two individuals, starting with the late Dr. Phil Cook of the EPA’s Mid-Continent Ecology Division in Duluth, MN. The history of the issues addressed by the Minnesota Taconite Workers Health Study – going back to the 1970s – necessarily includes Dr. Cook and the key role he played. The investigators also give special recognition to the late Tom Rukavina, who was a strong legislative and personal advocate for the study, not only for the University of Minnesota but for the people of Minnesota’s Mesabi Iron Range.
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