Optimizing ammonia emissions for PM2.5 mitigation: environmental and health co-benefits in Eastern China

Abstract

Ammonia (NH3) is a key precursor of PM2.5, contributing to the formation of secondary inorganic aerosols and playing a crucial role in haze events. However, current bottom-up emission inventories in China often underestimate NH3 emissions, particularly with significant uncertainties in urban areas. This study developed a “top-down” iterative algorithm that integrates the IASI satellite observations with the WRF-Chem model to optimize bottom-up NH3 emissions, and further quantified the impacts of source-specific emission reductions on PM2.5 pollution. The result reveals that the updated NH3 emissions in Eastern China for 2016 amounted to 4.2 Tg yr−1, 27.3 % higher than prior estimations. The optimized NH3 emissions peak in summer at 463.1 Gg month−1, with agricultural sources accounting for 85 %, while winter emissions drop to 217 Gg month−1 when the contribution from non-agricultural sources (e.g., industry, vehicle) significantly increases. The optimized NH3 emission significantly improved the simulation of both total column and surface NH3 concentrations, with improvements in magnitude (31 %–42 %) and variations (17 %–55 %). Sensitivity simulations show that a 30 %–60 % reduction in NH3 emission led to decreases of 1.5–8.8 µg m−3 in city-level PM2.5 concentrations and the potential effect of reducing non-agricultural emissions is comparable with that from agricultural sources. Furthermore, the NH3 reduction positively impacts public health, resulting in a 6.5 %–10.3 % decrease in premature deaths attributed to PM2.5 exposure. Our study evaluated NH3 emissions from various sources in Eastern China, emphasizing the impact of reducing non-agricultural ammonia emissions on air quality and public health benefits.