Decadal Trends in Wet Sulfur Deposition in China Estimated From OMI SO 2 Columns

Long‐term (from 2005 to 2016) trends in wet SO 4 2− deposition across China are assessed using Ozone Monitoring Instrument (OMI) SO 2 columns within the planetary boundary layer. The models for estimating monthly SO 4 2− deposition from precipitation in eight ecological regions are constructed based on SO 2 columns and ground‐based measurements. An accuracy assessment shows that the models achieve highly precise predictive values for monthly deposition ( R  = 0.93, with a relative/absolute error of −0.1/0.3 kg S · ha −1  · month −1 ). In terms of spatial distribution, SO 4 2− deposition shows substantial variations across China, ranging from 0.9 to 63.9 kg S · ha −1  · year −1 , with an average of 10.4 kg S · ha −1  · year −1 . Additionally, wet SO 4 2− deposition shows significant seasonal variations, increasing from January to July and then decreasing thereafter. Regarding long‐term trends, the wet SO 4 2− deposition in northern, central, and southern China decreased at rates of 0.009, 0.001, and 0.0009 kg S · ha −1  · month −1 , respectively. In contrast, Inner Mongolia, Qinghai‐Tibet, and northwest and northeast China showed increasing deposition trends. In general, the wet SO 4 2− deposition in 2016 decreased by 4.3% from that in 2005 on a national scale, indicating that air quality policies to control SO 2 emissions have had some effects on wet SO 4 2− deposition.