Regional simulation of anthropogenic sulfur over East Asia and its sensitivity to model parameters

We discuss a series of simulations of anthropogenic sulfur over East Asia with a SO2/So(4)(2-) chemistry-transport model driven in on-line mode by a regional climate model. Sensitivity to OH and H2O2 concentration, cloud parameters. SO2 dry deposition and emission strength is analyzed and the different components of the sulfur budget are examined. The SO2 and SO42- column burdens show pronounced variability at temporal scales from seasonal to synoptic and sub-daily, with SO2 and SO42- behaving differently due to the interplay of chemical conversion, removal and transport processes. Both SO2 and SO42- show marked spatial variability, with emission being the dominant term in regulating the SO2 spatial distribution. The atmospheric SO2 and SO42- amounts show close to a linear response to surface emission. Aqueous phase SO2 --> SO42- conversion and wet removal are the primary factors that regulate the SO42- amounts, with dry deposition and gas phase SO2 --> SO42- conversion being of secondary importance. Aqueous phase conversion and dry deposition are the dominant loss mechanisms for SO2 The model shows low sensitivity to variations in OH, H2O2, and cloud parameters, while the sensitivity to prescribed dry deposition velocity is more pronounced. Overall, our results are in line with previous modeling studies and with very limited available observations.