AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Aerosol Characterization over the Southeastern United States Using High Resolution Aerosol Mass Spectrometry: Spatial and Seasonal Variation of Aerosol Composition, Sources, and Organic Nitrates
NGA LEE NG, Lu Xu, Sriram Suresh, Hongyu Guo, Rodney J. Weber, Georgia Institute of Technology
Abstract Number: 491 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract We performed year-long comprehensive characterization of ambient aerosol in both rural and urban sites in the southeastern US as part of Southeastern Center for Air Pollution and Epidemiology (SCAPE) study and Southeastern Oxidant and Aerosol Study (SOAS) by using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and an Aerosol Chemical Speciation Monitor (ACSM). Organic aerosol (OA) accounts for more than half of NR-PM1 mass concentration regardless of sampling sites and seasons. Positive matrix factorization (PMF) analysis on the HR-ToF-AMS data resolved various OA sources. More-oxidized and less-oxidized oxygenated organic aerosol are dominant fractions (47-79%) of OA in all sites. Isoprene-derived OA is only deconvolved in warmer months and contributes 18-36% of total OA. Hydrocarbon-like OA and cooking OA are important but not dominant sources of total OA in urban sites. Biomass burning OA concentration has a larger enhancement in winter and correlates well with brown carbon.
We applied three independent methods to estimate the contribution of particulate organic nitrates to ambient OA in the SE US based on the HR-ToF-AMS measurements. The nitrate functionality from organic nitrates is estimated to contribute 63-100% of total measured nitrates in summer. Further, the contribution of organic nitrates to total OA is estimated to be 5-12% in summer, suggesting that organic nitrates are important components in the ambient aerosol in the southeastern US. The spatial distribution of OA is investigated by comparing simultaneous HR-ToF-AMS measurements with ACSM measurements at two different sampling sites. OA is found to be spatially homogeneous in summer. However, the homogeneity is less in winter. Finally, results from our short-term measurements with advanced instruments are compared to results from long-term measurements of basic air quality indicators from the SEARCH network. This comparison not only tests the robustness of the short-term measurements but also provides insights in interpreting long-term measurements.