Benefits of refined NH3 emission controls on PM2.5 mitigation in Central China

Atmospheric ammonia (NH3) is one of the most crucial precursors of secondary inorganic aerosols. However, its emission control is still weakness over China. NH3 emission inventories of 2015 with and without considering a set of refined emission reduction strategies covering seven major NH3 emission sources were constructed in Central China. GEOS-Chem model simulations were conducted to quantify the benefits of NH3 emission reduction on PM2.5 mitigation in four typical months (January, April, July and October). The results showed that these control strategies could reduce approximately 47.0% (152 Gg) of the total NH3 emissions in Hubei Province, with the agricultural (livestock and fertilizer application) source being reduced the most (133 Gg). NH3 had a significant nonlinear relationship with sulfate, nitrate, ammonium and PM2.5. NH3 emission reduction exerted less effect on sulfate mitigations (the annual average sensitivity was 4.5%), but it obviously alleviated nitrate, ammonium and thus PM2.5, with the annual average sensitivities of 81.9%, 34.8% and 22.0%, respectively. The average provincial concentrations of PM2.5 were alleviated by 11.2% in January, 10.6% in October, 10.2% in April and 9.3% in July through NH3 emission reduction by 47.0%. The reduction benefits were more pronounced in high NH3 emission areas, such as Yichang, with the PM2.5 reduction of 14.4% in January. This research could provide scientific support for formulating NH3 emission reduction policies to further mitigate PM2.5 pollution.