Characterization of aerosol composition and sources in the greater Atlanta area by aerosol mass spectrometry

Nga Lee Ng, Georgia Institute of Technology Main Campus, School of Chemical and Biomolecular Engineering, School of Earth and Atmospheric Sciences, School of Civil and Environmental Engineering, Atlanta, United States, Lu Xu, California Institute of Technology, Pasadena, CA, United States, Sriram Suresh, Georgia Institute of Technology, Atlanta, GA, United States, Rodney J Weber, Georgia Institute of Technology, School of Earth and Atmospheric Sciences, Atlanta, United States, Karsten Baumann, University of North Carolina at Chapel Hill, Department of Environmental Sciences and Engineering, Chapel Hill, United States and Eric S Edgerton, Atmospheric Research & Analysis, Inc., Cary, NC, United States
Abstract:
An important and uncertain aspect of biogenic secondary organic aerosol (SOA) formation is that it is often associated with anthropogenic pollution tracers. Prior studies in Atlanta suggested that 70-80% of the carbon in water-soluble organic carbon (WSOC) is modern, yet it is well-correlated with the anthropogenic CO. In this study, we deployed a High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and an Aerosol Chemical Speciation Monitor (ACSM) at multiple sites in different seasons (May 2012-February 2013) to characterize the sources and chemical composition of aerosols in the greater Atlanta area. This area in the SE US is ideal to investigate anthropogenic-biogenic interactions due to high natural and anthropogenic emissions. These extensive field studies are part of the Southeastern Center for Air Pollution and Epidemiology study (SCAPE). The HR-ToF-AMS is deployed at four sites (~ 3 weeks each) in rotation: Jefferson Street (urban), Yorkville (rural), roadside site (near Highway 75/85), and Georgia Tech site (campus), with the urban and rural sites being part of the SEARCH network. We obtained seven HR-ToF-AMS datasets in total. During the entire measurement period, the ACSM is stationary at the GIT site and samples continuously. We perform positive matrix factorization (PMF) analysis on the HR-ToF-AMS and ACSM data to deconvolve the OA into different components. While the diurnal cycle of the total OA is flat as what have been previously observed, the OA factors resolved by PMF analysis show distinctively different diurnal trends. We find that the “more-oxidized oxygenated OA” (MO-OOA) constitutes a major fraction of OA at all sites. In summer, OA is dominated by SOA, e.g., isoprene-OA and OOA with different degrees of oxidation. In contrary, biomass burning OA is more prominent in winter data. By comparing HR-ToF-AMS and ACSM data during the same sampling periods, we find that the aerosol time series are highly correlated, indicating the regional nature of aerosols in the Atlanta area. Taken together, results from these extensive field studies provide invaluable insights into the sources and processing of aerosols in the greater Atlanta area. The effects of anthropogenic emissions on biogenic SOA formation at multiple sites in the region and in different seasons will be discussed.
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