[Sulfur Sources and Oxidation Pathways in Summer Aerosols from Nanjing Northern Suburbs Using S and O Isotopes]

The sulfur and oxygen isotopic compositions of sulfate in PM were determined by EA-IRMS to study the sulfur sources and oxidation formation pathways of sulfates in PM from Nanjing northern suburbs during July 2014. The results indicated that δ S values of sulfate ranged from 1.7‰ to 4.8‰ with an average of 3.2‰±1.0‰, while δO values ranged from 7.5‰ to 12.9‰ with an average of 9.3‰±1.7‰. Comparing the δ S values of aerosol sulfate and potential pollution sources, we concluded that the sulfur source of PM was mainly local coal combustion and vehicle exhaust. In addition, the secondary sulfate was dominant in PM, and 59.3% of the formation of the secondary sulfate was caused by SO homogeneous oxidation. In addition, the heterogeneous oxidation of SO in the atmosphere was dominated by ferrous iron oxidation in excess O. The main mechanisms of homogeneous oxidation include oxidation in the presence of electric discharge (presumably forming O) and NO.