Benefits of refined NH₃ emission controls on PM_2.5 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 PM_2.5 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 PM_2.5. NH₃ emission reduction exerted less effect on sulfate mitigations (the annual average sensitivity was 4.5%), but it obviously alleviated nitrate, ammonium and thus PM_2.5, with the annual average sensitivities of 81.9%, 34.8% and 22.0%, respectively. The average provincial concentrations of PM_2.5 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 PM_2.5 reduction of 14.4% in January. This research could provide scientific support for formulating NH₃ emission reduction policies to further mitigate PM_2.5 pollution.