Searching for evidence of acid-catalyzed enhancement of secondary organic aerosol formation using ambient aerosol data |
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| Authors: | Roger L Tanner Kenneth J Olszyna Eric S Edgerton Eladio Knipping Stephanie L Shaw |
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| Institution: | 1. Key Laboratory of Western China''s Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China;2. College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China;3. State Key Laboratory of Cryospheric Science/Tien Shan Glaciological Station, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China;4. State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China;1. School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom;2. Center of Excellence in Environmental Studies, King Abdulaziz University, Jeddah, 21589, Saudi Arabia;3. Department of Environmental Sciences, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia;4. Faculty of Science, Alexandria University, 21526 El Shatby, Alexandria, Egypt;1. Key Lab of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an 710061, China;2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an 710061, China;3. University of Chinese Academy of Sciences, Beijing 100049, China;4. Department of Environmental Science, Xi''an Jiaotong University, Xi''an 710049, China |
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| Abstract: | Laboratory experiments suggest that strong acids promote formation of enhanced levels of secondary organic aerosol (SOA), and organic aerosols may contribute to the health impacts of fine PM. We report results from examining hourly speciated fine particle data for evidence of ambient aerosol acidity-catalyzed SOA formation, as indicated by larger increases in the concentrations of organic aerosol mass occurring on days and in locations where more acidic aerosol (lower NH4+/SO4= molar ratios) exists. Data sets from the southeastern U.S. were examined for which hourly acidity of PM2.5 aerosols could be estimated, and for which hourly organic carbon (OC) content had been measured simultaneously. Within-day organic aerosol changes during selected periods were statistically related to concurrent aerosol acidity levels estimated from nitrate-corrected ammonium-to-sulfate ratios. Data from the Look Rock, TN, TVA/IMPROVE site for mid-July to mid-August 2004 showed average compositions frequently as acidic as NH4HSO4, however, no apparent increases in OC levels with increasing aerosol acidity were observed, even when OC] changes were compared with time-delayed aerosol acidity estimates. SEARCH network data (2003–2004) for rural Centreville, AL (CTR) and Yorkville, GA (YRK) sites were also examined. Warm-season acidity levels were higher at CTR than at YRK, and daytime levels exceeded those at night at both sites. At the YRK site no consistent positive correlations were found between changes in OC or TC levels and aerosol acidity, even with time lags up to 6 h. Aerosol acidity at this site, however, is relatively low due to nearby agricultural sources of NH3. In contrast, during selected periods from April to October 2004, at CTR, 6-h lagged OC changes were weakly correlated with daytime, nitrate-corrected NH4+/SO4= molar ratios, but distinguishing this apparent relationship from meteorological effects on measured OC levels is challenging. |
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