Reducing PM2.5 and secondary inorganic aerosols by agricultural ammonia emission mitigation within the Beijing-Tianjin-Hebei region, China

The contribution to fine particulate air pollution (PM2.5) from ammonia emissions has been proven to be significant. In China, agricultural sources contribute to the majority of ammonia emissions. It is necessary and valuable to explore air quality improvements caused by the mitigation of agricultural ammonia emissions. The purpose of this study was to quantify the reduction effects on PM2.5 and secondary inorganic aerosols by performing air quality simulations based on the developed agricultural ammonia emission inventory at the county-level within the Beijing-Tianjin-Hebei (BTH) region. The results demonstrated that the total NH3 emission in the BTH region was 1625.03 Gg in 2015. Livestock manure spreading represented 58% of the total emissions (941.79 Gg NH3), while synthetic fertilizer applications accounted for the remaining 42% of the emissions. Spatially, the agricultural ammonia emissions were generally distributed over the southern BTH regions (Handan and Shijiazhuang) due to the intensive agricultural activities in this area. Temporally, the agricultural ammonia emissions peaked during summer, consistent with variations in temperature and agricultural practices. Compared to the baseline scenario, the annual average PM2.5 concentrations in the BTH region were reduced by 2.57%, 5.08%, and 5.71%, respectively, under the Progressive (NH3 emission cut by 21.26%), Stringent (NH3 emission cut by 45.58%), and Complex (NH3 emission cut by 46.63%) scenarios. Moreover, under the same conditions, secondary inorganic aerosols such as sulfate, nitrate, and ammonium were alleviated by 2.94-6.85%, 3.45-17.9%, and 4.24-23.32%, respectively. The results confirmed that mitigating ammonia emissions could lead to the considerable reduction of nitrate, followed by ammonium. In contrast, the impact on sulfate was relatively limited. This study could provide helpful and reliable evidence to determine effective mitigation measures and control strategies for policy makers.