Declining precipitation acidity from H_2SO_4 and HNO_3 across China inferred by OMI products

摘要

The long-term trend of precipitation acidity (PA) resulting from H2SO4 and HNO3 is analysed across China from 2005 to 2016 based on Ozone Monitoring Instrument (OMI) SO2 and NO2 columns, measured precipitation amounts, and ground measurements of SO42- and NO3- concentrations in precipitation. PA showed substantial variations across China, exhibiting an average of 0.88 keq ha(-1) yr(-1) in 2016. The spatial variation in SO42- deposition than that in NO3- deposition was closer to the spatial variation in PA, contributing 78.7% of the PA throughout China. Eastern China had significantly higher PA values than western China with four hotspots in the Yangtze River Delta (YRD) and Pearl River Delta (PRD), northern China (NC) and the Sichuan Basin (SCB). In eastern China, the PA values increased by 5.0% between 2005 and 2007 and then decreased by 34.3% in 2016, while the PA values in western China increased by 14.7% between 2005 and 2012 and then decreased by 2.0% in 2016. For the four hotspots, the SO42- to NO3- ratio (S/N) decreased; moreover, the PA decreased in NC, PRD and SCB but slightly increased in the YRD.