Abstract:With the continued advancement of air pollution control in China,reducing ammonia (NH3) emissions has emerged as a critical pathway for further mitigating PM2.5 pollution.The latest Air Quality Continuous Improvement Action Plan issued by the State Council emphasizes the progressive control of atmospheric ammonia pollution.However,previous studies have primarily focused on the nonlinear effects of NH3 emissions on PM2.5 mass concentrations at individual regional scales,lacking a comprehensive assessment of regional differences in mitigation effectiveness,associated health risks,and economic losses.Moreover,although the health impacts of PM2.5 have been extensively studied,the specific contribution of NH3 emissions to PM2.5-related health burdens and economic costs in China remains insufficiently quantified.Given that secondary inorganic aerosols (SIAs) account for 30％—50％ of PM2.5 mass in eastern China,with ammonium as a key component,quantifying the role of NH3 emissions is essential for developing effective control strategies.
To address these gaps,this study employs the GEOS-Chem chemical transport model and the GEMM to systematically evaluate the impacts of NH3 emission reductions on PM2.5 mass concentrations,health risks,and economic losses across three major urban agglomerations in eastern China—the Beijing-Tianjin-Hebei (BTH),Yangtze River Delta (YRD),and Pearl River Delta (PRD) regions—during 2020.A series of sensitivity experiments with NH3 emission reduction rates ranging from 20％ to 100％ were conducted to characterize the nonlinear responses of PM2.5 and its inorganic components.
The results show that PM2.5mass concentrations exhibit a pronounced nonlinear response to NH3emission reductions.As the reduction rate increases from 20％ to 100％,the annual mean PM2.5 mass concentration in eastern China decreases by 3.55％—35.50％.This nonlinearity is primarily driven by substantial decreases in ammonium and nitrate,while sulfate showsrelatively limited variation due to ammonia availability and gas-aerosol partitioning processes.Sulfate formation is generally not ammonia-limited except under extremely ammonia-poor conditions,whereas nitrate formation is highly sensitive to NH3 levels.
The effectiveness of NH3 emission reductions varies significantly across regions and seasons.In winter (January),under ammonia-rich conditions,PM2.5 reductions are initially limited.However,once critical thresholds are exceeded (greater than 60洅?浲潥牤敵?瑴慩牯杮攠瑩敮搠?慨湥搠?晒敄愠獡楮扤氠敐?慄洬浡潮湤椠慧?浥楡瑴楥杲愠瑴楨潡湮?瀸漰氅椠捩楮攠獴?e BTH),substantial decreases in PM2.5 are achieved,reflectinga transition from ammonia-rich to ammonia-limited regimes.In contrast,during summer (July),the PRD exhibitsa weak PM2.5 response even under high reduction scenarios,due to lower baseline SIA mass concentrations,higher temperatures favoring gas-phase partitioning,and differing meteorological conditions.Seasonal analysis further indicates that northern regions are more sensitive to NH3 reductions in winter,while southern regions show greater sensitivity in spring and autumn.
Health risk assessments indicate that PM2.5 exposure was associated with approximately 178.03—539.38 thousand premature deaths across the three regions in 2020,of which 22％—38％ were attributable to NH3 emissions.The YRD region experiences the highest health burden,at approximately 1.3—1.5 times that of the BTH,due to its dense population and higher baseline PM2.5 levels.Corresponding economic losses are estimated at 151.6—813.7 billion CNY,accounting for 1.37％—4.06％ of regional GDP.Moreover,health benefits increase nonlinearly with increasing emission reductions,with substantial gains observed beyond the 60％ reduction threshold.This nonlinear response highlights the importance of achievingdeep emission reductions to maximize public health benefits.
Thesefindings provide scientific support for developing region-specific NH3 emission control strategies and offer insights into balancing environmental protection with socioeconomic development.Continuous year-round NH3 control is recommended for ammonia-sensitive regions such as the YRD;for the BTH,deep reductions exceeding 80％ in winter or integrated multi-pollutant control strategies are necessary;and for the PRD,priority should be given to wintertime pollution control.Future studies should expand spatial coverage,consider multi-pollutant interactions,and incorporate cost-benefit analyses to infor
