Diurnal Variation of Organic Carbon Sources in Georgia

Yuan Cheng (1), MEI ZHENG (1), Xiuying Zhao (1), Wenyan Shi (1), Xiaolu Zhang (1), Rodney J. Weber (1), Eric S. Edgerton (2), and James J. Schauer (3)

(1) School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA (2) Atmospheric Research & Analysis, Inc., Cary, NC (3) University of Wisconsin-Madison, Madison, WI

     Abstract Number: 569
     Last modified: May 13, 2010

Abstract
Organic carbon is a major component of PM2.5 in the southeastern United States. The present study was a part of the August Mini-Intensive Gas and Aerosol Study (AMIGAS) in Georgia, in which 8-hour Hi-vol PM2.5 samples were collected during summer 2008 at one urban site and one rural site in Georgia. PM2.5 samples from day and night were analyzed for organic carbon (OC), elemental carbon (EC), and about 100 individual organic compounds including some important tracers. A chemical mass balance model based on molecular markers (CMB-MM) was applied to determine the relative contribution of major sources to ambient OC. There was no significant diurnal variation for PM2.5 during the study period. However, a clear diurnal pattern was observed for OC and EC. OC was higher during the day, mainly contributed by the emissions from gasoline engine exhaust and the formation of secondary organic aerosol (SOA). In contrast, EC was higher at night, primarily due to emissions from diesel engine exhaust and also other combustion processes such as biomass burning. Most organic tracers exhibited clear diurnal variations. For example, higher levels of hopanes and steranes were found during the day, while an obvious increase of levoglucosan and PAHs was observed at night. Tracers from secondary formation tend to be more abundant or slightly higher during the day. Primary tracers from combustion related sources are significantly higher at the urban site. However, the difference in secondary components was less significant, indicating a relatively homogeneous distribution of SOA on a regional scale. It is interesting to note that concentrations of cholesterol, a typical tracer for meat cooking, are consistently higher at the rural site, especially during the daytime. This suggests it is very likely that there are additional sources for cholesterol at the rural site.