Spatial and seasonal trends in biogenic secondary organic aerosol tracers and water-soluble organic carbon in the southeastern United States.

Twenty-four hour integrated filter samples of fine particulate matter (PM2.5) were collected from May 2004 to April 2005 at one rural site and three urban sites located in the southeastern United States. Filters were extracted and analyzed for both biogenic secondary organic aerosol (SOA) tracers via gas chromatography-mass spectrometry (GC-MS), and water-soluble organic carbon (WSOC) concentrations. The tracers reported in this study include isoprene-derived 2-methylthreitol and 2-methylerythritol, as well as pinene-derived cis-pinonic acid. The mean ambient concentrations ranged from 21.7 to 94.3 ng/m3, 5.31 to 17.9 ng/m3, and 1.87 to 3.18 microgC/m3 for 2-methyltetrols (sum of 2-methylerythritol and 2-methylthreitol), cispinonic acid and WSOC, respectively. Distinct spatial distributions were observed for all tracers with the highest concentration at the rural site and the lowest level at a coastal site. Although 2-methyltetrols were small fractions of WSOC, varying from 0.35% at an urban site to highest fractions of 1.09% at the rural site, WSOC exhibited significant correlation with 2-methyltetrols during summer, suggesting isoprene SOA makes an important contribution to WSOC. 2-Methyltetrols had the highest concentrations during the summer,when high temperature, intense solar radiation, and high ozone level occurred. However, no obvious seasonal variation was found for cispinonic acid. Between inland sites WSOC was more spatially homogeneous than the 2-methyltetrols, suggesting that WSOC was produced from a variety of mechanisms.