Significant reduction of PM2.5 in eastern China due to regional-scale emission control: evidence from SORPES in 2011–2018

Abstract

Haze pollution caused by PM_2.5 is the largest air quality concern in China in recent years. Long-term measurements of PM_2.5 and the precursors and chemical speciation are crucially important for evaluating the efficiency of emission control, understanding formation and transport of PM_2.5 associated with the change of meteorology, and accessing the impact of human activities on regional climate change. Here we reported long-term continuous measurements of PM_2.5, chemical components, and their precursors at a regional background station, the Station for Observing Regional Processes of the Earth System (SORPES), in Nanjing, eastern China, since 2011. We found that PM_2.5 at the station has experienced a substantial decrease (−9.1 % yr⁻¹), accompanied by even a very significant reduction of SO₂ (−16.7 % yr⁻¹), since the national “Ten Measures of Air” took action in 2013. Control of open biomass burning and fossil-fuel combustion are the two dominant factors that influence the PM_2.5 reduction in early summer and winter, respectively. In the cold season (November–January), the nitrate fraction was significantly increased, especially when air masses were transported from the north. More NH₃ available from a substantial reduction of SO₂ and increased oxidization capacity are the main factors for the enhanced nitrate formation. The changes of year-to-year meteorology have contributed to 24 % of the PM_2.5 decrease since 2013. This study highlights several important implications on air pollution control policy in China.