Importance of sulfate emission to sulfur deposition at urban and rural sites in China

Throughfall (TF) and wet only (WO) deposition along with SO2 and sulfate (SO42−) concentration in air at 4 urban and rural sites in southwestern China were monitored in order to understand the role of different forms of sulfur (S) emission to the S deposition and its effect in China. The sites were located in Chongqing, Hunan, and Guizhou provinces. S deposition at the most polluted site reached 15 g S m− 2 yr− 1. At three of the sites, located in the vicinity of several emission sources, dry S deposition is 2.1–4.2 times that of wet deposition, which is significantly higher than what is found in most other parts of the world.Main components in airborne particles (PM10) are (NH4)2SO4 and CaSO4 at the highly polluted Tie Shan Ping (TSP) site. Dust particles of gypsum (CaSO4) in the air are partly due to direct emission and partly from the reaction of calcium oxides and carbonates with sulfuric acid in the air. To illustrate the importance of sulfate emission to total S deposition we analyzed the source of S deposition based on both measurements and models. Results indicated that direct emission of SO42− particles could account for high proportion in total S deposition at the three most polluted sites.