Generation and Characterization of Hardwood Smoke Inhalation Exposure Atmospheres

Aerosol Science and Technology

ISSN: 0278-6826 (Print) 1521-7388 (Online) Journal homepage: https://www.tandfonline.com/loi/uast20

Jacob D. McDonald , Richard K. White , Edward B. Barr , Barbara Zielinska , Judith C. Chow & Eric Grosjean

To cite this article: Jacob D. McDonald , Richard K. White , Edward B. Barr , Barbara Zielinska , Judith C. Chow & Eric Grosjean (2006) Generation and Characterization of Hardwood Smoke Inhalation Exposure Atmospheres, Aerosol Science and Technology, 40:8, 573-584, DOI: 10.1080/02786820600724378 To link to this article: https://doi.org/10.1080/02786820600724378

Published online: 01 Feb 2007.

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Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=uast20 Aerosol Science and Technology, 40:573–584, 2006 Copyright c American Association for Aerosol Research ISSN: 0278-6826 print / 1521-7388 online DOI: 10.1080/02786820600724378 Generation and Characterization of Hardwood Smoke Inhalation Exposure Atmospheres

Jacob D. McDonald,1 Richard K. White,1 Edward B. Barr,1 Barbara Zielinska,2 Judith C. Chow,2 and Eric Grosjean3 1Lovelace Respiratory Research Institute, Albuquerque, New Mexico, USA 2Desert Research Institute, Reno, Nevada, USA 3Daniel Grosjean and Associates, Inc., Ventura, California, USA

INTRODUCTION An inhalation exposure system and operating protocol were de- The National Environmental Respiratory Center (NERC) was veloped that resulted in consistent achievement of targeted expo- established to conduct laboratory research that improves our un- sure concentrations of hardwood smoke without compromising the derstanding of the contributions of individual air contaminants desire to include multiple phases of a burn cycle. A conventional, noncatalyzed stove was operated in a temperature-controlled room and their combinations to the health effects associated with ex- with a three-phase (kindling, high burn, and low burn) cycle. posures to complex air pollution mixtures. The NERC research Equally sized wood of similar moisture content was loaded in a strategy (described at www.nercenter.org) includes the conduct consistent fashion each day of the study. A stable and control- of a series of inhalation toxicology studies (laboratory expo- lable dilution system was employed that involved simultaneous sures of rodents) of common source emissions having different, withdrawal of smoke from a primary dilution tunnel. Exposure operators utilized real-time measurements of particulate matter but overlapping, compositions. Both the composition of the ex- (PM), CO, and stove temperature, along with operational experi- posure atmospheres and a range of health effects are measured ence, to gauge when adjustments to dilution air or the firebox were in detail using identical protocols, and the results are compiled necessary. Dilutions of smoke were controlled in four separate in- into a composition-concentration-health response database that halation atmospheres with daily average particle mass concentra- will be utilized for statistical and other exploration of the data. tions of 30, 100, 300, and 1000 µg/m3. Each of these atmospheres was characterized in detail, including gas, semivolatile, and par- The first NERC study, termed “Contemporary Diesel Emis- ticle phases. Gas phase hydrocarbons were composed mostly of sions” (circa 2000), has been completed and the composition carbonyls (especially furans) and acids (especially low molecular (McDonald et al. 2004) and several health responses have been weight aliphatic acids). Several classes of gas-phase semivolatile reported (Harrod et al. 2003, 2005; Campen et al. 2003; Reed organics were measured, with the highest proportions of material et al. 2004; Barrett et al. 2004). The generation and characteriza- in classes of polycyclic aromatic hydrocarbons and methoxy phenols. The particle phase was primarily organic carbon (>90%) tion of exposures for the second study, hardwood smoke (HWS), with small amounts of ions, elements, and black carbon. Approx- are described here. The health responses are being reported in imately 15% of the organic carbon was identified and quantified, separate articles. with the largest contribution of material from sugars and sugar Typical inhalation exposure systems rely on a steady and re- derivatives. producible production of a test material (e.g., HWS) that can be set and maintained at a target concentration (or dilution). In these types of systems, continuous monitoring by an appropriate technique can be used to give system operators feedback to maintain dilutions. This approach is complicated when the test material Received 7 November 2005; accepted 23 March 2006. is produced in variable concentrations throughout an exposure This work was supported by the National Environmental Respira- period, such as emissions from diesel engines operated on a tran- tory Center, which was funded by numerous industry, state, and federal sient cycle as reported for the first NERC study (McDonald et al. sponsors, including the U.S. Environmental Protection Agency, U.S. Department of Energy, and U.S. Department of Transportation. This 2004). In that study the engine cycle was continuously repeated manuscript does not represent the views or policies of any sponsor. every 20 min. Because the cycle was reproducible, the system The exposure system was operated and data were collected by Mark operator could utilize averages of measurements of particulate Gauna and Richard Mossman. Ben Myren, of Myren Consulting, Inc. matter (PM) obtained over several repeating cycles (e.g., three, (Colville, WA), assisted in the development and characterization of the repeated 20-min cycles gavea1hsample, the total exposure burn cycle. Address correspondence to Jacob D. McDonald, 2425 Ridgecrest time was 6 h) to monitor the dilutions. A similar approach was Dr. SE, Albuquerque, NM 87108, USA. E-mail: [email protected] taken in a wood smoke study (using pinyon pine), reported by

573 574 J. D. MCDONALD ET AL.

Tesfaigzi et al. (2002), where several PM measurements (ap- METHODS proximately every 10–30 min over a 6-h period) were utilized to adjust dilutions. In that study, smoke was generated in a single Wood Smoke Generation and Exposures operating mode, with wood being continuously added through- Construction of the system and procedures for operating the out the exposure period and the stove operated with the air in- appliance were modeled, in part, after the U.S. Environmental take at a constant setting. Because of the variability in wood Protection Agency’s (EPA) Method 28A, “Standards of Per- emissions during that study, operation of the system was labor formance for New Stationary Sources; New Residential Wood intensive and the result showed considerable variability in the ex- Heaters; Final Rule” (U.S. EPA 1988), and the Washington State posure concentrations. Others have attempted to produce a more Uniform Building Code Standard 31-2. The final design of the stable wood smoke atmosphere by burning aerosolized wood system is shown in Figure 1. The design and operation of the shavings in a flow-through furnace (Zelikoff et al. 2002). An ap- system are described below. proach that eliminated fluctuations in wood smoke concentration HWS was generated by burning a mix of hardwood (genus would be desirable from an operational standpoint, but would Quercus, species mixed and not specified by vendor) in a non- not be representative of the true variations in the composition of certified wood stove (Pineridge Model 27000; Heating Energy wood smoke as it is predominantly generated and exists in the Systems, Inc., Clackamas, OR) having a 0.06-m3 firebox and environment. a customized sliding gate air intake damper. A custom damper The HWS study was designed to include multiple phases wasdeveloped because the stock damper had an automatic valve (kindling, low, and high burn rates) of a single burn cycle dur- that would open and shut the damper based on temperature at ing each 6-h exposure day. The goal was to have simultaneous the front of the stove box. Over time, this automatic damper did dilutions (yielding daily integrated average PM concentrations not operate correctly and was replaced with a manual damper of 30, 100, 300, 1000 µg/m3) that could be reproduced from that would allow better control of the system. The dimensions day to day, despite the complication of variability through- of the fabricated damper were 1.5 cm × 6.5 cm. out each burn phase. A further complication was the day-to- The stove was isolated in an ∼55-m2 building that was tem- ◦ day variability. Variability in wood stove emissions can be perature controlled between 18–32 C throughout the study by linked to several factors, including the configuration and op- filtered forced-air cooling (in the summer). Seasoned hardwood eration of the stove, burn rate, type of wood, moisture of that was uniformly split (∼50 cm × 8 cm) from rounds and wood, configuration of flue, draft on flue, and barometric pres- included bark was obtained from a private vendor located in sure (McCrillis et al. 1989, 1990). An approach was devel- Potosi, Missouri. Upon arrival, the moisture content of ∼10 oped that minimized the impact of these factors, including sentinel pieces of wood was measured with a calibrated electri- R standardization of the burn cycle, enclosure of the flue in cal resistance moisture meter (J-2000; Delmhorst Instruments, the same building as the stove with a fixed draft across the Towaco, NJ). The moisture (20–25% dry weight) was main- top of the flue, and maintenance of homogenously sized and tained throughout the course of the study by storing the wood ◦ split wood stored in a cold room (10–15◦C) under controlled in a temperature- (∼15 C) and humidity-controlled (∼90%) conditions. room. Exposure atmosphere composition in the exposure cham- The stove was operated over a three-phase burn cycle that bers was assessed as described previously (McDonald et al. spanned the 6-h exposure period. The fire was started (which 2001, 2004). The approach included assessments of PM con- initiated exposures) with unprinted/unbleached newspaper (end- centration and composition; particle number count and size dis- rolls obtained from Albuquerque Journal, Albuquerque, NM) tribution; elements (metals and associated analytes); inorganic and hardwood (same wood type used for entire test) split into sulfate, nitrate, and ammonium; PM organic and elemental car- small (e.g., 5–10 cm in width) pieces. The three burn phases in- bon ([EC] also termed as black carbon); and speciated organic cluded kindling (∼15–20 min), a high burn rate (∼90 min with compounds (including alkanes, alkenes, alkynes, cycloalkanes/ ∼4–6 kg of wood), and a low burn rate (remainder of exposure cycloalkenes, furans, phenols, sugars, acids, carbonyls, volatile period with an additional ∼4–6 kg of wood) controlled by the aromatic compounds, polycyclic aromatic hydrocarbons [PAH], air intake damper. For the high burn rate, the sliding damper was oxygenated PAH, hopanes, and steranes). Gaseous NH3, NOx, open (maximum air intake) and then closed down to an aperture ∼ × SO2, CO, and CO2 were also measured. Several of the com- of 0.3 6.5 cm during the low burn cycle. The burn rate (loss ponents were semivolatile organic compounds (SVOCs) that of wood mass/time) was measured during the exposure period existed simultaneously in the gas and particle phase. Because by a platform scale (Mountain Scales, Inc., Denver, CO) that this characterization resulted in thousands of compositional data the stove was placed on. Transition from kindling to high burn points, it is not practical to publish the data in their entirety. In- to low burn was based on a combination of the approximate stead, this article describes the experimental methodology and time interval described above. Through a series of prestudy test- summarizes major findings. The entire data set for the study is ing and evaluations, it was determined that at those time points available on the NERC web site (www.nercenter.org). ∼75% of the wood mass had been burned. WOOD SMOKE INHALATION ATMOSPHERES 575

FIG. 1. Schematic of woodstove, ﬂue, dilution/transit lines, and exposure chamber for conducting inhalation exposures to hardwood smoke. Note that four exposure levels were used, and only one chamber is shown for illustration.

The flue was a 15.2-cm triple-wall insulated solid pack steel after being scrubbed by passage through HEPA and charcoal- chimney, extending ∼3mfrom the platform scale, that transi- impregnated pre-filters to remove particles and volatile organics. tioned into a double-walled chimney up to a height of ∼4m.The At the primary dilution point, the smoke traveled through a 5-cm top of the flue was maintained in an enclosed space and had a diameter line for 4 m before it expanded to a 15.2-cm line, where 60-cm (cross-sectional diameter) shroud located around the top the flow rate was approximately 900 L/min. 20 cm that maintained constant flow of air across the top of the At a location 7.6 m from the flue extraction point, four paral- stack. This shroud maintained a flow sufficiently high to exhaust lel probes of diameters ranging from 0.6 cm outer diameter (OD) the majority of the wood smoke to a waste smoke oxidizer while for the low exposure chamber to 2.5 cm O.D. for the high cham- maintaining the draft induced on the wood stove below 0.02 cm ber were used to extract smoke for transfer to the chambers. The of water measured when the stove was not operating. A minor range in probe diameters allowed maintenance of similar flow portion of the smoke was extracted for transfer to the dilution velocities at all of the extraction points even though volumet- tunnel at a flow rate of ∼30 L/min with a 2.5-cm probe located ric extraction flows varied from approximately 10–100 L/min. ∼30.5 cm from the top of the flue. This 180-cm line was main- After extraction from the main dilution plenum, the diameter tained at approximately 300◦Ctominimize water condensation of each transfer line expanded to 5 cm. Each transfer line had and thermophoretic particle losses during transit. At the termina- additional dilution and bypass air for further dilution. Mass flow tion of the heated line, a series of several dilution and air bypass controllers that were interfaced into the computer monitoring legs served to quickly dilute the smoke down to ∼20–23◦C. system controlled the final dilution/bypass air on each cham- Dilution was conducted with outside air maintained at ∼20◦C ber. The transfer lines from the 15.2-cm dilution plenum to the 576 J. D. MCDONALD ET AL. exposure chambers were ∼5mlong. Because of practical con- tor (Langan CO measurer; Langan Instruments, San Francisco, siderations, the lengths of the transfer lines were similar, but CA). The real-time data was utilized by the exposure operator not identical. The small variations in the length of the transfer (along with PM measurements) as an indicator of dilution. The lines (up to 2 m) translated to differences in transit time among chemical cell was purchased directly from Langan and placed exposure levels of only fractions of a second. in a flow-through capsule immediately downstream of the filters Exposures were conducted in 2-m3 flow-through exposure utilized for determining PM. Total NOx were measured using a chambers (H2000, Hazleton Systems, Maywood, NJ). Material chemiluminescent analyzer (Model 200A NOx Analyzer; Pollu- passed through these chambers at approximately 500 L/min, tion Instruments, San Diego, CA). Both NOx and CO analyzers yielding a material residence time within the chamber of about were calibrated prior to each study using National Institute of 4 min. These chambers were designed to enhance the unifor- Standards and Technology traceable standards. Techniques for − −2 mity of the distribution of test material. The spatial variation of the collection and analysis of SO2,NO3 /SO4 , and NH4+ have the HWS PM within these chambers was determined to be less been described elsewhere (Chow et al. 1998). than 10% when determined as previously described (McDonald Speciated gas phase organic compounds were determined by et al. 2001). The exposures included five treatment groups: four mass spectrometric (MS) analysis of samples (alkyne, alkane, exposed to different dilutions of HWS and one to clean air as a alkene, aromatic, furan) collected in electropolished canisters, control. trapped on KOH impregnated filters (acids), or trapped on The system dilutions were based on 6-h average target con- dinitrophenylhydrazine- (DNPH)-impregnated silica gel car- centrations of 30 (low), 100 (mid-low), 300 (mid-high), and 1000 tridges (for carbonyl and dicarbonyl). Canister samples were (high) µg/m3 HWS PM. At the highest exposure level, the dilu- analyzed by gas chromatography (GC)/MS, and both KOH im- tion from the flue was determined to be ∼300:1 by measuring pregnated filters and DNPH cartridges were analyzed by liquid CO directly from the flue and in the exposure chamber. Because chromatography-diode array-MS. the system was on a three-phase burn cycle, the concentrations inside the exposure chambers varied throughout each exposure period. As a result, the primary emphasis of the exposure sys- Particle Mass tem operator was to maintain targeted dilution splits among the PM was collected on 47-mm Teflon impregnated glass fiber exposure groups (e.g., 3:1 difference in dilution between the (T60A20; Pall-Gelman, East Hills, NY) filters. Pre- and post- mid-low and mid-high levels). These splits were monitored by a exposure filter weights were measured gravimetrically immedi- combination of real-time PM and CO, determined as described ately prior to and after exposures using a Mettler MT5 microbal- below. ance located in the exposure laboratory. Over the 6-h exposure duration, filter samples were collected hourly (60-min samples) from the two highest exposure levels and three times (120-min Exposure Characterization samples) from the two low levels. One filter sample per day was Detailed assessment of the composition of the exposure atmo- collected from the control chamber. PM is reported as the total spheres at all exposure levels, including quality assurance and PM measured in the exposure chambers. HWS PM is the total quality control, was conducted as described in detail previously PM minus the PM measured in the control chamber. Although air (McDonald et al. 2004). Because of practical constraints, de- flowing through the control chamber was filtered, small amounts tailed assessments were only conducted periodically (e.g., three of PM (0–15 µg/m3) were measured in the control chamber due times per exposure level) throughout the course of the study. to the presence of the rodents. Assuming that the rodent con- Table 1 summarizes the measurements, collection technique, tribution to PM was the same in each exposure chamber, the measurement technique, and analysis allocation (several of the control PM value was subtracted from the exposure chamber samples were analyzed by collaborating laboratories). Gravi- PM to yield HWS PM. metric mass was measured from each exposure level each day of Because filter-based PM data were utilized for monitoring the study. Carbon monoxide and total hydrocarbons were mea- and controlling PM concentrations during exposures, it was not sured 5–10 times per exposure level, and the remaining measure- practical to equilibrate the filters prior to and after sampling in a ments were made approximately three times per exposure level. conditioning chamber at a specified temperature and humidity. Methods are described briefly below, with particular attention Some samples were taken to assess the difference in measured to methods that differed slightly from those reported previously PM concentration after filter conditioning for 24 h at 23◦C and (McDonald et al. 2004). 40% relative humidity prior to and after sampling, and results did not differ by more than 10%. Gas Phase To characterize the potential vapor artifact on the PM mea- Concentrations of CO were determined using a photoacoustic surement, several samples were collected where either an gas analyzer (Innova 1312; California Analytical Instruments, XAD-4 coated concentric vapor denuder was placed upstream of Irvine, CA). Real-time CO was measured simultaneously in the Pallflex filter or a TefloTM filter (Pall-Gelman) was used. The each exposure atmosphere with a modified chemical cell detec- vapor denuder serves to remove vapors prior to contact with the TABLE 1 Summary of exposure atmosphere characterization measurements and measurement conditions Collection Sample flow Analytical Analysis Analysis Collection device Collection media point rate (L/m) instrument allocation Gravimetric mass Aluminum in-line filter holder TIGF Chamber/Plenum 4 MB LRRI Continuous mass Dust-Trak nephelometer NA Chamber 2 NA LRRI Nitric oxides Chemiluminescence analyzer NA Chamber 0.4 NA LRRI CO/CO2/THC Photoacoustic analyzer NA Chamber 1 NA LRRI THC Flame ionization detector NA Chamber 1 NA LRRI Organic/black carbon Aluminum in-line filter holder Quartz filter Plenum 20 TOR DRI Ions (sulfate/nitrate/ammonium) Aluminum in-line filter holder Quartz filter Plenum 20 IC, AC DRI SO2 Aluminum in-line filter holder K2CO3-impregnated filter Chamber 2–5 IC DRI NH3 URG denuder (20 cm, 4 channel) Citric acid-coated Chamber 5 AC DRI Metals and other elements Teflon in-line filter holder Teflon filter Plenum 20 ICPMS/ICPOES WSLH Volatile hydrocarbons (C1-C12)Volatile organic sampler Electropolished canister Chamber 0.1 GCMS/GCFID DRI Volatile carbonyls Volatile organic sampler DNPH cartridge Chamber 0.3 LC/DAD/MS DGA, Inc. Volatile organic acids Aluminum in-line filter holder KOH-impregnated quartz filter Chamber 1–2 LC/DAD/MS DGA, Inc. Semivolatile/fine particle organics Tisch environmental PUF sampler Quartz filter/PUF/XAD-4/PUF Plenum 80 GCMS LRRI Semivolatile/fine particle organics URG denuder (60 cm, 8 channel) XAD-coated/filter/PUF/ Plenum 80 GCMS LRRI XAD-4/PUF List of Abbreviations: Chemical species:CO= carbon monoxide; CO2 = carbon dioxide; SO2 = sulfur dioxide; NH3 = ammonia; THC = total hydrocarbons. Instruments/collection devices:MB= microbalance; NA = not applicable; TOR = thermal/optical reflectance; IC = ion chromatography; ICPMS = inductively coupled plasma mass spectrometry; ICPOES = inductively coupled plasma optical emission spectroscopy; GCMS = gas chromatography mass spectrometry; GCFID = gas chromatography flame ionization detector; DNPH = dinitrophenylhydrazine; LC/DAD/MS = liquid chromatography/diode array/mass spectrometry; PUF = polyurethane foam; GCMS/LCMS = gas chromatography mass spectrometry/liquid chromatography mass spectrometry; URG = URG Corporation; MOUDI = micro orifice uniform deposit impactor; SMPS = scanning mobility particle sizer; CPC = condensation particle counter. TIGF = Teflon impregnated glass fiber filter. AC = automated colorimetry. Organizations: LRRI = Lovelace Respiratory Research Institute; DRI = Desert Research Institute; WSLH = Wisconsin State Laboratory of Hygiene; DGA, Inc. = Daniel Grosjean and Associates, Inc. 577 578 J. D. MCDONALD ET AL.

filters to prevent or reduce vapor adsorption artifacts. In each the filters. Technique 2 has a higher collection capacity, but is case, the alternative PM measurement was collected simultane- subject to positive (adsorption of vapor-phase to filter) and nega- ously and at the same flow rate as the Pallflex filter. tive (desorption of particle organics from the filter) artifacts. The Real-time PM was measured using a Model 8520 DustTrak data reported here are from technique 2 (filters = particle-phase photometer (TSI, Inc., Minneapolis, MN) to assess system sta- and sorbent = vapor-phase). Technique 1 revealed inconsistent bility and serve as an indicator of chamber concentration in order results in gas-particle partitioning (showed breakthrough), and to adjust dilutions for achieving the target mass concentration. had poor scaling between exposure levels because (due to lim- The DustTrak response was calibrated for HWS PM by making ited sample capacity) the samples were taken at specific times simultaneous gravimetric measurements and deriving a correc- during the burn cycle, not over the entire three-phase burn cy- tion factor for the DustTrak response based on filter weights. cle. Technique 2 was collected over the entire burn cycle, and showed good scaling between different exposure levels. Prior to extractions, samples were spiked with a range of PM Composition deuterated or 13C-labeled internal standards that included PAH, ForPMcomposition (not including speciated organics and alkanes, phenols, acids, and sugar derivatives (detailed list de- metals), samples were collected on Pallflex 47-mm diameter, scribed in McDonald et al. 2004). The denuder was extracted heat treated, pre-baked (to remove contaminant organic car- and analyzed separately from the filter cartridge to allow direct bon) quartz-fiber filters. Following collection, one-half of the quantification of the portions in the vapor and particle phase. filter was extracted in water and the extract was analyzed for Filter and sorbent cartridge extractions were conducted in a NO3–/SO4–2 by ion chromatography and NH4+ by colorime- MARS-X microwave extractor. Two sequential extractions were try (Chow et al. 1998). On the second half of the filter, organic conducted: dichloromethane (for filters) or 90:10 hexane:ether carbon (OC) and EC content were analyzed by the IMPROVE (for sorbent cartridge) followed by acetone. After extraction, thermal/optical reflectance method described by Chow et al. samples were concentrated by rotoevaporation to ∼4mLand (1993). To convert the measured OC response to organic matter further concentrated to ∼0.5 mL under a gentle stream of ni- (OM), a correction factor of 1.4 was applied. This correction trogen. Samples were then split and either analyzed by GC/MS factor takes into account noncarbon elements such as hydrogen directly (neutral and nonpolar compounds) or analyzed after be- and oxygen that are not measured by the analytical technique but ing derivitized by either silation (sugar derivatives and sterols) contribute to the mass of PM. Although other conversion fac- or methylation (acids) as described previously (McDonald et al. tors that apply to wood smoke have been proposed (e.g., Turpin 2004). and Lam 2001), this conversion factor yielded good agreement between the sum of measured species and total particle mass in this study. The same conversion (1.4) also yielded good com- Particle Size parisons with gravimetric mass in other wood smoke emission Particle size was measured using a ten-stage micro-orifice- characterization studies (McDonald et al. 2000). Elements were uniform deposit impactor ([MOUDI]; MSP Corp., Minneapolis, determined in acid digestions of Teflo filters by inductively cou- MN). The impactor was operated at a flow rate of 30 L/min, pro- pled plasma (ICP)-MS and ICP-optical emission spectroscopy viding particle size data from 0.05–10 microns in aerodynamic (for Si and S) as described by McDonald et al. (2004). diameter. The chemical composition was assessed for impaction Vapor-phase SVOCs and particle-phase organic compounds stages with cutpoints below 5.6 µm (50% cut-off point) as de- were collected by two separate techniques: (1) a XAD-coated scribed previously by Kleeman et al. (2000) and McDonald et al. denuder (vapor phase) followed by a Teflon-coated glass-fiber (2002). The larger sizes were not analyzed, both because they filter/polyurethane foam/XAD-4/polyurethane foam cartridge accounted for a very small amount (<3%) of the mass and be- (particle phase) and (2) a Teflon-coated glass-fiber filter (particle cause they are not in the respirable size range of a rodent. The phase) followed by the polyurethane foam/XAD-4/polyurethane top MOUDI stages (down to 5.6 µm) were lightly greased to foam cartridge (vapor phase). Both approaches were used be- collect any larger particles that could have bounced and created cause the techniques have complementary performance charac- positive artifacts at lower stages. The stages at 3.16, 1.78, 1.00, teristics. The denuder, when conditions are appropriate, yields 0.54, 0.37, 0.148, 0.105, and 0.054 µm were used without grease, the best operational definition of the vapor-particle split because with a quartz-fiber (same type used for carbon analysis described the vapor phase is removed before it can adsorb to the filter. below) after-filter to collect particles smaller than 0.054 µm. PM In addition, when the denuder is used the back-up sorbent is to be analyzed for OM/BC and inorganic ions was collected on counted as particle-phase, effectively correcting for desorption pre-baked aluminum substrates, and samples for metal analysis of particle-phase components from the filter to the sorbents. were collected on pre-cleaned (McDonald et al. 2004) Teflon In addition to several potential limitations of technique 1 re- membrane filters. Analysis of these samples is described in the ported by Kamens et al. (1999), the denuder does not function following sections. properly if it is overloaded with material that saturates the active Particle number size distribution was measured using a scan- sorbent sites, leading to breakthrough of vapor-phase SVOCs to ning mobility particle sizer ([SMPS]; Differential Mobility WOOD SMOKE INHALATION ATMOSPHERES 579

FIG. 2. Real-time particle mass concentration during two separate operations of the three-phase burn cycle. Both of these resulted in an average particle mass concentration of approximately 1 mg/m3.

Analyzer Model 3080, Condensation Particle Counter Model at all exposure levels. Not shown here, but comparing the TEFLO 3025, TSI, Inc.). The SMPS was operated at a sample flow rate (Teflon membrane) with the Pallflex (Teflon-coated glass fiber) of 0.3 L/min and a sheath flow rate of 3 L/min. SMPS scans revealed little to no difference in the measured particle mass were collected several times throughout each exposure day at concentration. In addition, measurements of wood smoke PM each exposure level. The total scan time was 3 min. Because the with a vapor denuder up-stream resulted in an ∼20% decrease particle size changes throughout each phase of a burn cycle, the in measured PM, suggesting that vapor adsorption accounted for SMPS scans are partially skewed because not all particle sizes approximately this much of the mass on filter. could be measured simultaneously. The gaseous portion of HWS in these exposure atmospheres was composed of gaseous CO (max of ∼13 ppm at high exposure level) and volatile organics (max of ∼3 ppm at high expo- RESULTS sure level), with low to nondetectable concentrations of NOx and Figure 2 gives two examples (at high exposure level) of real- SO2. The volatile organics were almost entirely composed of car- ∼ time traces of PM during the three-phase burn cycle. As ex- bonyls ( 30% of volatile organic compounds [VOC]) and acids pected, the PM concentrations fluctuated throughout the day ac- cording to the burn cycle, and the highest concentrations in the chamber were observed during the low burn rate phase. Figure 2 also illustrates that there was variability in each phase from day to day. Both of the examples shown resulted in average PM concentrations of 1000 µg/m3. Because of this, characterizations were conducted multiple times at each exposure level to ensure that the range and magnitude of the variability of individual constituents were characterized. Figure 3 gives data from measurements taken on three separate days for CO, THC, several organic compounds along with calcium and iron. These were all obtained from the High exposure level on days where the particle mass concentrations were within 20% of the 1000 µg/m3 target. Overall there was reasonable agreement from day to day, especially for CO and THC, which were present in the highest concentrations. The components that were present in low concentrations (e.g., ng/m3-µg/m3) were the most variable from day to day. The composition of the HWS at each exposure level is given in Figure 4 and Table 2. Note the average PM concentrations were within 10% of the target at all exposure levels. In addition, the standard deviation shows that the day-to-day vari- FIG. 3. Concentration of total hydrocarbons (THC), carbon monoxide (CO), and several minor components of the wood smoke atmosphere obtained from the ability in average PM concentrations was low. Including over High exposure chamber on three separate days. The individual data are averages 9 months of continuous operation, over 90% of the exposure integrated over a 6-h burn cycle. In general, the trace components showed the days were within 15% of the target PM exposure concentration most variability in concentration from day to day. 580 J. D. MCDONALD ET AL.

FIG. 4. Summary composition (by weight percent) of clean air, and four exposure levels of hardwood smoke.

(∼60% of VOC). The single largest class within the carbonyls metals and other elements. The most abundant elements were were the furans (∼40% of total carbonyl), which were dominated calcium, potassium, and zinc, with small (<100 ng/m3 at high by 2-methyl furaldehyde. Other carbonyls in large abundance exposure level) but detectable amounts of iron and aluminum. included methyl-ethyl-ketone, acetone, and acetaldehyde. Acids As expected based on laboratory and field studies of the were almost entirely (90%) composed of aliphatic compounds, composition of wood smoke (Rowell 1984; Rogge et al. 1998; mostly due to the large abundance (∼1.5 mg/m3 at high level) McDonald et al. 2000; Schauer et al. 2001; Fine et al. 2002), the of acetic acid. HWS OM contained substantial concentrations of sugars (arib- The fractional abundance of the primary PM constituents inose, xylose), sugar derivatives (especially levoglucosan), and − −2 (EC, OM, NO3 /SO4 ,NH4+, metals) showed that PM was com- methoxylated phenols. PAHs were present in HWS; however, posed of nearly 100% OM at all exposure levels. Fifteen percent they only accounted for a small total portion of the exposure of this OM was able to be quantified and attributed to specific an- atmosphere (less than 0.5% of PM). alytes as described below. In the clean air control, the OM likely PM in the HWS exposure showed particle sizes from 0.25– consisted of a combination of rodent dander and exhaled organic 0.35 µm median diameter, with the largest particle size observed vapor that adsorbed onto the quartz filter and was measured as at the lowest dilution (highest concentration). The slightly larger organic carbon. Electron microscopic analysis (not shown here) size with lower dilution was somewhat expected, as similar ob- revealed that the HWS PM was primarily composed of amor- servations were reported for differences in particle size with phous and spherical organic droplets. Because of their volatility, dilution for diesel exhaust (Reed et al. 2004). Mass distributions it was not possible to obtain suitable electron micrographs of the are presented as the fractional mass amount (dm/m total) for each HWS PM because the analyses are obtained under vacuum that incremental size range. Because the MOUDI stages were 50% smears the PM. In addition to OM, there was ∼5% EC and 2–3% cut-off points and there was mass on each stage that overlapped TABLE 2 Summary of hardwood smoke exposure atmosphere composition Exposure atmosphere composition Units Clean air Low Mid-low Mid-high High Notes Particle mass µg/m3 6.4 ± 6.9 40.5 ± 9.2 113.3 ± 21.8 319.7 ± 43.9 1041.1 ± 123.5 Particle count particle/cm3 0.0 1.4 × 105 1.1 × 105 2.2 × 105 3.4 × 105 Non-methane VOC µg/m3 177.6 ± 10.4 221.1 ± 72.9 397.5 ± 132.5 1429.8 ± 09.9 3455.0 ± 557.2 Ammonia µg/m3 139.3 ± 2.3 60.7 ± 0.9 57.4 ± 0.9 50.1 ± 1.0 54.9 ± 1.2 Sulfur dioxide µg/m3 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 Carbon monoxide µg/m3 229.0 ± 31.0 801.6 ± 14.4 1832.3 ± 43.6 4580.8 ± 01.6 14887.6 ± 832.3 Nitrogen monoxide µg/m3 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 Nitrogen dioxide µg/m3 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 Particle composition Elemental carbon µg/m3 0.2 ± 0.1 2.9 ± 0.2 12.4 ± 0.7 24.9 ± 1.4 42.6 ± 2.7 Organic carbon µg/m3 2.8 ± 0.2 40.3 ± 5.7 107.2 ± 3.6 281.2 ± 12.3 907.7 ± 29.5 Ammonium µg/m3 0.2 ± 0.2 0.3 ± 0.1 0.5 ± 0.3 1.5 ± 0.3 2.2 ± 0.3 Sulfate µg/m3 0.0 ± 0.2 0.1 ± 0.1 0.3 ± 0.3 0.4 ± 0.3 0.6 ± 0.3 Nitrate µg/m3 0.0 ± 0.2 0.0 ± 0.1 0.3 ± 0.4 0.6 ± 0.4 0.9 ± 0.3 Elements (metals and µg/m3 0.0 0.1 0.4 1.0 2.2 n = 43 associated elements) Non-methane volatile organic compounds Isoalk-ane/ene µg/m3 14.4 9.0 24.0 20.1 36.7 n = 7 Alkene µg/m3 3.4 4.6 15.5 44.1 86.3 n = 14 Alkane µg/m3 26.2 28.6 38.1 92.1 171.8 n = 10 Aromatic µg/m3 5.6 7.3 14.2 41.5 96.5 n = 21 Halogenated µg/m3 4.2 6.0 4.5 4.0 11.9 n = 17 Carbonyls µg/m3 48.8 83.5 165.9 408.4 1325.1 n = 95 Acids µg/m3 75.0 82.1 135.4 819.7 1726.6 n = 36 Volatile carbonyls Aliphatic carbonyl µg/m3 1.6 2.1 1.6 4.2 5.4 n = 27 Alkanal µg/m3 23.2 31.6 51.2 103.1 281.4 n = 17 Alkenal µg/m3 0.5 2.6 4.7 7.9 21.1 n = 5 Aromatic aldehyde µg/m3 1.2 1.4 2.2 3.9 10.7 n = 9 Dicarbonyl µg/m3 0.2 5.7 9.2 26.0 83.6 n = 9 Hydroxy carbonyl µg/m3 2.8 6.8 18.1 36.8 107.5 n = 4 Furans µg/m3 0.4 7.1 30.5 135.0 515.2 n = 5 Ketone µg/m3 16.2 18.7 33.1 62.7 193.9 n = 10 Other carbonyl µg/m3 2.6 5.4 11.0 18.5 66.3 n = 8 Oxocarbonyl µg/m3 0.0 2.1 4.1 10.2 40.0 n = 5 (Continued on next page) 581 582

TABLE 2 Summary of hardwood smoke exposure atmosphere composition (Continued) Exposure atmosphere composition Units Clean air Low Mid-low Mid-high High Notes Volatile organic acids Aliphatic acid µg/m3 73.1 75.1 130.1 793.7 1669.1 n = 21 Alkenoic acid µg/m3 0.0 1.1 1.3 11.2 23.4 n = 5 Aromatic acid µg/m3 0.2 0.2 0.1 0.6 1.1 n = 6 Hydroxy acid µg/m3 1.6 5.6 3.7 13.8 31.7 n = 2 Oxoacid µg/m3 0.0 0.2 0.1 0.4 1.3 n = 2 Vapor phase semi-volatile organic compounds (by class) Sterol ng/m3 4.0 1.6 1.3 1.5 4.5 n = 4 Sugar derivative ng/m3 163.9 143.9 175.6 613.3 1217.6 n = 10 Methoxylated phenol ng/m3 11.5 784.1 2064.8 7836.4 21481.4 n = 14 Furans ng/m3 0.0 633.0 993.6 2102.2 5991.3 n = 1 Acid ng/m3 83.1 500.8 825.5 1436.2 5439.3 n = 10 Alkane ng/m3 42.5 88.6 56.5 135.2 221.6 n = 11 Polycyclic aromatic hydrocarbons ng/m3 69.6 1287.6 2168.7 4506.1 11060.1 n = 58 Oxygenated polycyclic ng/m3 1.4 0.0 6.4 53.2 93.7 n = 8 aromatic hydrocarbons Particle phase organic compounds (by class) Sterol ng/m3 0.3 11.5 50.1 277.3 2173.4 n = 4 Sugar derivative ng/m3 184.8 1829.2 9184.9 43599.5 107379.7 n = 10 Methoxylated phenol ng/m3 0.0 5.5 113.6 682.5 3068.8 n = 14 Furans ng/m3 0.0 0.0 0.0 66.9 135.7 n = 1 Acid ng/m3 153.1 101.3 228.2 988.6 310.8 n = 10 Alkane ng/m3 21.2 32.9 56.5 239.9 821.2 n = 11 Polycyclic aromatic hydrocarbons ng/m3 16.6 12.6 39.9 159.3 465.2 n = 58 Oxygenated polycyclic ng/m3 8.3 4.1 5.9 20.0 31.6 n = 8 aromatic hydrocarbons

Note:Ndenoted number of individual compounds combined for sums. Values are averages of measurements from multiple days. Errors are standard deviations among multiple measurements, and are only shown for averages, not sums, of compound classes. WOOD SMOKE INHALATION ATMOSPHERES 583

FIG. 5. Size-selective chemistry of hardwood smoke sampled from the high exposure level (1 mg/m3 particle mass). in size from the higher and lower cut points, aerodynamic diam- bound together by lignin (methoxylated phenols) polymers. eters are represented as the geometric mean between impactor Wood (all plants) also includes several elements, especially cut points. Figure 5 shows the particle size by composition for a calcium, potassium, zinc, and iron that are all functioning el- sample collected from the high exposure level. The particle size ements in living systems (e.g., calcium/potassium important for by composition mirrored the overall PM composition, mostly osmotic balance in plants). During combustion wood is decom- composed of OM across the entire size range. The elements posed and distilled to produce large proportions of sugar/lignin and inorganic ions were not observed below ∼0.2 µmorabove derivatives and some metals (elements). In the gas-phase furans, 1 µm. They were distributed relatively evenly between 0.2 and carbonyls/dicarbonyls, and methoxyphenol derivatives were ob- ∼1.0 µm. served in this study, as was previously reported in hardwoods Particle number size distribution, as previously reported by Hays et al. (2002), changes throughout different portions of the wood smoke cycle. Figure 6 shows three sample particle number scans obtained from the mid-high exposure level at different portions of the burn cycle. Median particle number diameters spanned from approximately 20–150 nm, depending on the burn conditions. The three particle sizes were obtained from different portions of the high and low burns. In general, the smaller particle sizes were observed during high burn conditions where more oxidative burn conditions likely occurred. The larger particle sizes were observed during the low burn conditions.

DISCUSSION Overall, the composition at all exposure levels was consistent with results of previous studies that have characterized emissions from wood smoke in the laboratory or field (Hillis 1962; Commins 1969; Rowell 1984; McCrillis et al. 1989; Rogge et al. 1998; McKenzie et al. 1994; McDonald et al. 2000; Schauer et al. 2001; Fine et al. 2002). The characteristic composition of wood FIG. 6. Representative particle number size distribution scans from different smoke is derived from the structure of wood, which is approxi- points in the burn cycle. In general, smaller particle sizes were observed during mately 60–70% cellulose (sugars such as pentose, arabinose) high burn (higher oxygen) conditions. 584 J. D. MCDONALD ET AL. by McDonald et al. (2000). Sugars and sugar derivatives such and Exacerbated Lung Disease to Pseudomonas aeruginosa Infection in vivo, as arabinose and levoglucosan along with primarily the syringol Toxicol. Sci. 83:155–165. (2,6-methoxyphenol) lignin derivatives accounted for large por- Hays, M. D., Geron, C. D., Linna, K. J., Smith, N. D., and Schauer, J. J. (2002). Speciation of Gas-Phase and Fine Particle Emissions from Burning of Foliar tions of the particle phase. Also observed as part of the particle Fuels, Environ. Sci. Technol. 36:2281–2295. phase were several sterols (including phytosteroids such as β- Hillis, W. E. (1962). Wood Extractives, Academic Press, New York. sitosterol as well as α-tocopherol [Vitamin E]). Kamens, R. M., Fan, Z., Myosoen, J., Odum, J., Hu, J., Coe, D., Zhang, J., Chen, While variability in emissions are inherently characteristic of S., and Leach, K. (1999). The Use of Denuders for Semivolatile Characteriza- wood burning cycles, and are desirable to include in an average tion Studies in Outdoor Chambers, in Gas and Particle Phase Measurements of Atmospheric Organic Compounds, Lane, D. A., ed., Overseas Publishers exposure to wood smoke, variations in the average emissions Association, Amsterdam, pp. 333–367. rates from day to day pose several problems for conducting re- Kleeman, M. J., Schauer, J. J., and Cass, G. R. (2000). Size and Composition peated controlled exposures. In this study, an exposure system Distribution of Fine Particulate Matter Emitted from Motor Vehicles, Environ. and operating protocol was developed that resulted in consistent Sci. Technol. 34:1132–1142. achievement of targeted exposure concentrations without com- McCrillis, R. C., Leese, K. E., and Harkins, S. M. (1989). Effects of Burn Rate, Wood Species, Moisture Content and Weight of Wood Loaded on Wood- promising the desire to include multiple phases of a burn cycle. stove Emissions; U.S. Environmental Protection Agency Contract 68-02- The system kept a constant small draw on the flue by keeping it 3992, EPA/600/2-89/025, Work Assignments 7 and 37, Research Triangle enclosed in a custom built cupola. The stove was operated in a Institute (EPA Project Officer: McCrillis, Air and Energy Engineering Re- temperature-controlled room to ensure that the temperature did search Lab, RTP, NC 27711). not change throughout the duration of the study. Equally sized McCrillis, R. C., and Burnet, P. G. (1990). Effects of Burn Rate, Wood Species, Altitude, and Stove Type on Woodstove Emissions, Toxicol. Ind. Health 6:95– wood of similar moisture content was loaded in a consistent 102. fashion each day of the study. A stable and controllable dilution McDonald, J. D., Zielinska, B., Fujita, E. M., Sagebiel, J. C., Chow, J. C., system was employed that involved simultaneous withdrawal of and Watson, J. G. (2000). Fine Particle and Gaseous Emission Rates from smoke from a primary dilution tunnel. Lastly, the exposure op- Residential Wood Combustion, Environ. Sci. Technol. 34(11):2080–2091. erators utilized real-time measurements of PM, CO, and stove McDonald, J. D., Costanzo, J., Barr, E. B., Mauderly, J. L., Schauer, J. J., Zielinska, B., Sagebiel, J. C., Chow, J. C., Grosjean, D., and Grosjean, E. temperature, along with operational experience, to gauge when (2001). Characterization of Laboratory Exposure Atmospheres for Health adjustments to dilution air or the firebox were necessary. By Effects Studies, Published by CD-ROM. In Proceedings of Air and Waste monitoring stove temperature, the system operator was able to Management Annual Conference, Orlando, FL, June 24–28, 2001. follow the combustion conditions each day, and make adjust- McDonald, J. D., Zielinska, B., Sagebiel, J. 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