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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 Generation and Characterization of Hardwood Smoke Inhalation Exposure Atmospheres 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. Submit your article to this journal Article views: 355 Citing articles: 17 View citing articles 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 phe- nols. 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 tech- nique 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).
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