Size distributions of particulate matter and PAHs from Nanjing in summer and autumn

Atmospheric aerosols with different size in Nanjing urban area were collected during the haze and non-haze periods in summer and autumn 2007, and PAHs concentration and distribution in the summer wheat straw-burning period was also characterized. Size distribution of the particles was bimodal with one peak at the range of 0.41-2.1 μm (accumulation mode) and another peak at the range of > 3.0 μm (coarse mode) in the two seasons except in haze days caused by the biomass burning. In contrast, a unimodal (accumulation mode) was found for the particles collected in the summer haze periods mainly due to emissions from the straw burning. Compared with those in the non-haze period, abundances of the low molecular weight (LMW) PAHs(3, 4-ring) increased by 41%, and enriched in fine particles (< 2.1 μm); while abundances of the high molecular weight (HMW) PAHs(5, 6-ring) do not present significant differences in size distributions during haze days. Because of the wheat straw burning, both the fine particles and LMW PAHs increased remarkably.