Organic molecular compositions and size distributions of Chinese summer and autumn aerosols from Nanjing: Characteristic haze event caused by wheat straw burning

Size-segregated aerosol samples were collected in urban Nanjing, China during summer and autumn of 2007 including a period of hazy days during June 1-5. Organic aerosols in the haze event were characterized by elevated concentrations of levoglucosan, high molecular weight (HMW) n-alkanes, and HMW fatty acids due to the emissions from field burning of wheat straw. In contrast, organic aerosols on nonhazy days were characterized by a predominance of fossil fuel combustion products. Levoglucosan (4030 ng m^-3), n-alkanes (1520 ng m^-3), fatty acids (2629 ng m^-3), and PAHs (57 ng m^-3) in the haze samples were 3-40 times more abundant than those innoneventsamples. Approximately 30-90%of the organics during the haze period can be attributed to wheat straw burning. Concentrations of particulate material (PM) mass, n-alkanes, and low molecular weight (LMW) PAHs showed a unimodal size distribution, peaking at 0.7-1.1 μm during the hazy days, and a bimodal distribution, peaking at 0.7-1.1 μm and 4.7-5.8 μm during nonhazy days. The geometric mean diameters (GMDs) of organic aerosols are larger in the fine mode(<2.1μm)during the hazy days, suggesting aerosols emitted from the wheat straw burning are larger than those from fossil fuel combustion, and fine particle coagulation and organic compound repartitioning were enhanced.