Source identification and size distribution of atmospheric polycyclic aromatic hydrocarbons during rice straw burning period

Atmospheric particulate and polycyclic aromatic hydrocarbon (PAH) size distributions were measured at a suburban area in central Taiwan during the rice straw burning and non-burning periods. Samples were acquired using a semi-volatile sampling train (PS-1 sampler) and a micro-orifice uniform deposit impactor (MOUDI). The collected materials were extracted and then analyzed by gas chromatograph/mass selective detector for 21 PAHs. The average total PAH concentrations of particulate and gaseous phases were 33.0 and 1160 ng m -3, respectively, in the rice straw burning period, which were higher than those on the non-burning days. Potential sources of PAHs were identified using the characteristic ratios. Benzo[a]pyrene/benzo[ghi]perylene ratio indicates the burning of rice straw is a significant source for PAH contribution at the sampling area. It also suggests that the rice straw burning primarily contribute fine particulate PAHs. Bimodal size distributions are obtained with a predominance of total PAHs in the accumulation mode during rice straw burning periods and in ultra-fine mode during non-burning periods. The particulate and particulate phase PAHs from rice straw burning are coarser than those from vehicle exhaust. The results also suggest that the amounts of PAHs per unit mass of particulate are less for the burning of rice straw than those of vehicle emissions.