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PM2.5 Pollution and Temperature Inversions: a Case Study in St Meteorology Senior Theses Undergraduate Theses and Capstone Projects 2018 PM2.5 Pollution and Temperature Inversions: A Case Study in St. Louis, MO Hannah R. Johnson Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/mteor_stheses Part of the Meteorology Commons Recommended Citation Johnson, Hannah R., "PM2.5 Pollution and Temperature Inversions: A Case Study in St. Louis, MO" (2018). Meteorology Senior Theses. 44. https://lib.dr.iastate.edu/mteor_stheses/44 This Dissertation/Thesis is brought to you for free and open access by the Undergraduate Theses and Capstone Projects at Iowa State University Digital Repository. It has been accepted for inclusion in Meteorology Senior Theses by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. PM2.5 Pollution and Temperature Inversions: A Case Study in St. Louis, MO Hannah R. Johnson Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa William Gutowski – Mentor Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa Elizabeth Lennartson – Mentor Minnesota Pollution Control Agency, St. Paul, Minnesota ABSTRACT Wintertime temperature inversions are partially responsible for some of the worst historical air pollution events as cold air pools are favorable for prolonged poor air quality episodes. The St. Louis metropolitan area in Missouri-Illinois has relevant problems with particulate pollution yet is under-studied. This case study examines the characteristics of an inversion layer along with additional meteorological parameters and their effects on PM2.5 air quality in St. Louis from November 22 to December 3, 2015. During the selected period, November 26 to December 1 PM2.5 Air Quality Index (AQI) daily values often exceeded levels the Environmental Protection Agency classifies as unhealthy for sensitive groups. Shallow surface temperature inversions were most common on less polluted days while strong temperature inversions with a base height around 950 mb persisted on more heavily polluted days. Variability in surface wind speed, wind direction, and relative humidity occurred mostly on less polluted days while values were consistent on more heavily polluted days. Precipitation only happened on the most heavily polluted days but showed no great impact of reducing pollution. Winds from the south on November 26 suggested transport of excess particulate pollutant was the cause of unhealthy PM2.5 levels that day, not temperature inversions. Strong temperature inversions contained these pollutants in St. Louis on November 27 to November 30. A surface pressure minimum north of St. Louis on December 1 produced a substantial change in wind direction on November 30, influencing eventual dispersion of pollutants. Further research is necessary to help fill in the knowledge gaps about air quality in the Midwest. ______________________________________________________________________________ 1. Introduction biodiversity, and human health. In 2016, 91% of the world population was living in Air pollution is an interdisciplinary problem places where the World Health that poses a severe threat to Earth’s climate, 1 Organization’s (WHO) air quality guideline to form. When an area of high surface levels were not met, with an estimated 4.2 pressure develops, wind speeds are low million premature deaths due to ambient air enough for recirculation and stagnant air, pollution in both urban and rural areas during increasing the longevity of a poor air quality the same year (WHO 2018). episode. Mortality is caused by exposure to ambient China is a commonly studied place for air air particles with an aerodynamic diameter of pollution meteorology due to its complex 2.5 micrometers or less, known as fine geographical terrain and influence from high particulate matter (PM2.5). These particles anthropogenic emissions. Wang et al. (2018) can be emitted directly from a local source or found that observation stations in China have as combustion particles from industrial higher PM2.5 concentrations during air emissions (EPA 2018). With penetration to stagnation events, defined as days without the lung barrier, particulate matter can enter precipitation and daily PM2.5 concentrations the blood system to cause cardiovascular and higher than its monthly average, occurring respiratory distress, both acute and chronic most frequently during autumn and winter. (EPA 2010, WHO 2018). The WHO 2005 air The study used a quantitative threshold based quality guideline limits are aimed to achieve on 10-meter (m) wind speed, boundary layer the lowest concentrations of particulate height and amount of precipitation to account matter as possible as there is no measured for the effect of terrain on meteorological threshold where no damage to human health conditions as the National Oceanic and occurs (WHO 2018). Atmospheric Administration’s (NOAA) threshold does not. The stability of the atmosphere is a critical component for understanding the severity of Taking the inversion layer into account, air quality. A stable atmosphere occurs Enzhong et al. (2015) focused their study on when a layer of warm air is above cooler air, Xingtai City, a Chinese urban area forming a temperature inversion as air surrounded by mountains. Results showed a temperature increases with height (NWS positive correlation between air quality and 2018). Vertical motion of an air parcel is the thickness of the inversion layer and a inhibited, trapping air pollutants close to negative correlation between air quality and Earth’s surface. temperature, dew point and wind speed within the inversion layer from 2013-2014. Temperature inversions are not the only The strongest inversions occurred in the meteorological influence on air quality. The winter with the weakest during the summer. atmosphere warms, dries and stabilizes Bahari et al. (2014) also noted the importance because of large-scale downward vertical of the strength of temperature inversions’ motion in the presence of an upper-level impact on air quality as this addition ridge of high pressure, typically at 500 indicated a well-fitting model for the millibars (mb). Cloud formation is restricted prediction of PM concentrations in Iran. in a temperature inversion layer, allowing an 2.5 increase in photochemistry for air pollutants 2 In the United States, the West Coast is a The Clean Air Act was established in the commonly studied area for air pollution due United States by the Environmental to the complex terrain of the Rocky Protection Agency in 1970 to address public Mountains and transport of Asian health issues and welfare risks posed by anthropogenic aerosols. The most frequent certain widespread air pollutants by air stagnation events occur in the summer and implementing National Ambient Air Quality autumn using an adjusted quantitative Standards (NAAQS) for each state to attain threshold to account for terrain (Wang et al. (EPA 2018). Regulations of anthropogenic 2018). A case study in Cache Valley, a emissions correlate with a negative trend in narrow area, surrounded by tall mountains the annual mean of total ambient air particles located in northern Utah and southern Idaho, from 1975-1986, though health risks from showed an increased probability of fine ambient air particles persisted, ranking temperature inversions during cold days St. Louis as the city with the 2nd highest during the winter, with a daily mean air mortality rate to due ambient air pollution temperature below -15℃ indicating certainty compared to 5 other U.S. cities (Dockery et for the occurrence (Wang et al. 2015). A al. 1993). The health risks from inhaling regression model was developed to estimate particulate matter in the 1980s and a decrease past PM2.5 concentrations to account for in PM2.5 concentrations (Dockery et al. 1993) missing upper-air measurements. Though are comparable to current identifiable health the model was merely a function of risks and a 41% decrease in the national temperature and did not include chemical PM2.5 air quality trend from 2000 to 2017 kinetics, it indicated increased concentration (EPA 2018). The St. Louis metropolitan area from the early 1980s through the early 1990s, was an exception, specified as nonattainment the same period with an increase of the for annual PM2.5 NAAQS in 2005 (EPA frequency of temperature inversions (Wang 2010). et al. 2015). With historical problems of particulate The effects of prolonged wintertime pollution in St. Louis and the enormous temperature inversions on air quality have influence of meteorological conditions for occurred outside of the West Coast, but there deviation in a region's air quality trend, the is a lack of research in these areas with need for research persists in this historical problems of air pollution. For underrepresented geographic area. This case instance, the St. Louis metropolitan area in study focused on a period during the Missouri-Illinois was plagued with a thick wintertime when the St. Louis metropolitan layer of smog for over a month during the area was experiencing persistent cold-weather season in 1939 due to the PM2.5 pollution to answer these questions: region’s heavy reliance on cheap, high sulfur 1) How frequently did temperature coal and continuous urban population inversions occur during this period? increase (O’Neil 2016). 2) How did the base height and strength of a temperature inversion on a 3 Figure 1. EPA classification of Air Quality Index (AQI)
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