Trends in secondary inorganic aerosol pollution in China and its responses to emission controls of precursors in wintertime

Abstract. The Chinese government recently proposed ammonia (NH3) emission reductions (but without a specific national target) as strategic option to mitigate fine particulate matter (PM2.5) pollution. We combined meta-analysis of nationwide measurements and air quality modeling identify efficiency gains by striking balance between controlling NH3 acid gas (SO2 NOx) emissions. found that PM2.5 concentrations decreased from 2000 2019, but annual mean still exceeded 35 µg m−3 at 74 % 1498 monitoring sites during 2015–2019. concentration its components were significantly higher (16 %–195 %) on hazy days than non-hazy days. Compared with values other components, this difference was more significant for the secondary inorganic ions SO42-, NO3-, NH4+ (average increase 98 %). While sulfate over period, no change observed nitrate ammonium concentrations. Model simulations indicate effectiveness 50 reduction aerosol (SIA) 2010 2017 in four megacity clusters eastern China, simulated month January under fixed meteorological conditions (2010). Although further declined 2020 including natural experiment substantial emissions COVID-19 pandemic, resulting SIA average 20.8 lower those 2017. In addition, greater reductions. Our findings persistent pollution China is limited gases, while an additional control would become important SO2 NOx progress.