Diurnal Variations of Organic Aerosol at Two Sites in Georgia, USA

MEI ZHENG (1), Xiuying Zhao (1), Wenyan Shi (1), Rodney Weber (1), Xiaolu Zhang (1), and James Schauer (2)

(1) Georgia Institute of Technology, Atlanta, GA (2) University of Wisconsin-Madison, Madison, WI

     Abstract Number: 464
     Last modified: January 12, 2010

Abstract
Organic carbon is a major component of fine particulate matter (PM2.5) in Atlanta, Georgia. Previous studies have focused on the 24-h samples from this area. In order to better understand the diurnal variations of organic aerosol especially its composition and sources, a summer campaign was conducted during summer 2008 (August 12-September 6) at one urban site and one rural site in Georgia. These Hi-vol PM2.5 samples were analyzed for organic carbon (OC) and elemental carbon (EC) with thermal-optical transmittance method while detailed speciation of organic aerosol was done by gas chromatograph/mass spectrometry (GC/MS), including alkanes, hopanes, steranes, polycyclic aromatic hydrocarbons (PAHs), fatty acids and resin acids. A few important organic tracers of biogenic secondary organic aerosols (SOA) were also measured including 2-methyltetrols, cis-pinonic acid and pinic acid.

Preliminary results indicated that clear day-night differences exist for some primary organic tracers, including wood burning tracers (levoglucocan and resin acids) and PAHs from incomplete combustion of carbonaceous materials with higher levels at nighttime. This pattern is not seen for biogenic secondary tracers, which in fact are slightly enriched during daytime, e.g., 2-methyltetrols and cis-pinonic acid. Distinct spatial distributions were observed for all tracers with higher concentrations at the urban site, including alkanes, hopanes, steranes, PAHs, biomass burning and secondary organic tracers except for 2-methyltetrols. It corresponds well with the observation of water soluble organic compounds (WSOC) which are mostly comprised of polar organic compounds from both anthropogenic and biogenic sources. On average, the urban-rural difference is by a factor of 2.5. This study shows that an urban site like Jefferson Street, Atlanta is not only enriched in primary pollutants but also secondarily formed organic aerosol especially substances from vehicular emissions.