Anthropogenic ammonia (NH3) emissions, largely from agriculture, severely impact environmental quality, causing air pollution, soil acidification, water eutrophication, and harming human and ecosystem health. The economic damage from agricultural NH3 emissions was substantial in the EU (US$55–114 billion in 2008) and the US (US$69–180 billion in 2011), primarily due to increased mortality from NH3-containing aerosols. High-income countries have implemented mitigation strategies, such as the Gothenburg Protocol and the EU's National NH3 Emission Ceilings directive. China, the world's largest NH3 emitter (9–13 Tg N year⁻¹ in the 2010s), with agriculture contributing over 80%, urgently needs mitigation due to low fertilizer nitrogen use efficiency (NUE), poor waste management, and increasing decoupling between crop and livestock production. The current clean air policy focusing on PM2.5, SO2, and NOx has limitations, highlighting the need to abate NH3 emissions for cost-effective PM2.5 control. Many NH3 abatement techniques also reduce methane (CH4) and nitrous oxide (N2O) emissions, offering climate co-benefits; however, NH3 reduction might increase rainfall acidity. China lacks policies to reduce NH3 emissions despite available measures, creating a need for a national assessment of mitigation potential, costs, and societal benefits to establish effective strategies and targets. This study utilizes an integrated assessment framework combining Coupled Human And Natural Systems (CHANS), GAINS, Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ), and exposure-response models to address this knowledge gap.

Existing literature highlights the significant environmental and health impacts of ammonia emissions, particularly from agriculture. Studies in the European Union and the United States have quantified the substantial economic costs associated with these emissions, primarily due to increased mortality and morbidity from particulate matter pollution. The Gothenburg Protocol and subsequent EU directives demonstrate a commitment to ammonia emission reduction in high-income countries. However, research on the cost-effectiveness and societal benefits of ammonia mitigation strategies, especially in large-scale agricultural systems like China's, has been limited. Previous studies have addressed ammonia emissions in China, but a comprehensive national-level assessment integrating various mitigation options and associated costs and benefits was lacking. This study fills this gap by providing a detailed analysis considering both technical and non-technical mitigation strategies.

This study employs an integrated assessment framework combining several models and datasets to analyze ammonia mitigation in China. The framework includes: 1. **Coupled Human And Natural Systems (CHANS) model:** This model simulates the interactions between human activities and natural systems, providing a comprehensive understanding of ammonia sources, emissions, and environmental fates. 2. **GAINS model:** This model helps estimate the abatement costs of implementing different NH3 mitigation strategies and options. It considers various factors, such as investment and operational costs. China-specific commodity prices from the China Agricultural Products Cost-Benefit Yearbook (2000–2018) are utilized, along with adjustments based on purchasing power parity (PPP) to ensure consistent monetary values. 3. **Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) model:** This model is used to assess the impact of NH3 reduction on PM2.5 concentrations. The model simulates the atmospheric processes involved in PM2.5 formation and dispersion. Specific equations (Eq. 8, 9, 10, 11) are employed to calculate health benefits based on the changes in PM2.5 concentrations and the Value of Statistical Life (VSL). 4. **Exposure-response models:** These models link changes in air pollution levels to health outcomes, allowing for quantification of the health benefits associated with reduced NH3 emissions. These models draw on established methodologies and data from sources such as the Global Burden of Disease project. 5. **Cost-effectiveness analysis (MACC):** This analysis is carried out using equation (6) to prioritize emission reduction strategies based on cost. The study considers a range of mitigation options, categorized for croplands (fertilizer management, urea reduction) and livestock (feed optimization, manure management, housing adaptation). The framework accounts for the potential impact of mitigation efforts on the acidity of precipitation, incorporating it into the overall societal benefit assessment (Equation 7). The study also employs scenario analysis, incorporating business-as-usual (BAU) and four mitigation scenarios (DIET, NUE, REC, and ALL) to project future emissions and assess the effectiveness of different mitigation pathways up to 2050. These scenarios reflect varying strategies for modifying human diet, improving nitrogen use efficiency (NUE), recycling livestock manure, and combining these approaches. Each scenario’s cost-benefit analysis is detailed with associated equations to illustrate methodologies. International comparison data from the EU, Canada, and the USA are utilized to contextualize the findings for China.

The study reveals a substantial technical mitigation potential for agricultural NH3 emissions in China (38–67%, or 4.0–7.1 Tg N). The estimated abatement costs are significantly lower than the projected societal benefits, resulting in substantial net economic benefits. Key findings include: * **Cost-effectiveness:** The total abatement cost is estimated at US$6–11 billion, while the total societal benefit is estimated to be US$18–42 billion. A significant portion (30%) of the emission reduction can be achieved at zero or negative cost by optimizing fertilizer application and animal feed. This suggests a high cost-effectiveness of NH3 mitigation in China. * **Mitigation potential:** The study projects that 38-67% of total agricultural ammonia emissions can be mitigated. Specific measures reveal significant potential for reduction across a range of crop and livestock systems, with the pig industry showcasing the largest potential. Significant percentages are possible for major crops like rice, wheat, and maize, underscoring the opportunity for widespread impact. * **Societal benefits:** The societal benefits substantially outweigh the abatement costs. These benefits are primarily derived from improved human health (reduced premature mortality from improved air quality) and ecosystem health (reduced soil acidification and water eutrophication), along with climate benefits (reduction in greenhouse gas emissions). While increased rainfall acidity is a potential negative effect, the overall societal benefits still far exceed costs. * **Mitigation pathways:** Scenario analysis shows that the 'ALL' scenario (combining dietary changes, improved NUE, and manure recycling) yields the greatest reduction in emissions (61%) but at the highest cost (US$11 billion in 2050). However, the societal benefits remain far higher than the costs even in this scenario. The 'DIET' scenario, focusing on dietary changes, shows the lowest cost due to its largely non-technical nature. * **International comparison:** China's NH3 mitigation potential (53%) is roughly double that of the EU27 (24%) and Canada (29%), reflecting the larger scale of emissions and the lack of implemented mitigation policies in China. However, China's unit abatement cost is lower, attributed to differences in farm sizes, labor costs, and agricultural mechanization levels. * **Prioritization:** The marginal abatement cost curve (MACC) shows that reducing urea-based N fertilizer and protein-rich animal feed are the most cost-effective initial strategies. Subsequent measures, such as improved manure management and housing adaptation, become progressively more expensive. * **Synergies:** The study also highlights synergies between NH3 mitigation and greenhouse gas reduction, with significant co-benefits possible through several mitigation strategies. However, manure recycling, while helpful for NH3 mitigation, might slightly increase N2O emissions, necessitating careful consideration.

The findings underscore the significant societal benefits of implementing agricultural NH3 mitigation strategies in China. The substantial economic advantages, far exceeding the abatement costs, suggest a compelling case for action. The study’s identification of cost-effective options, including zero-cost measures, makes ammonia reduction attainable even with resource constraints. The analysis of different mitigation pathways underscores the need for a holistic approach incorporating technical and non-technical measures. The dietary scenario highlights the substantial influence of consumption patterns on ammonia emissions, suggesting that promoting sustainable diets could play a significant role in reaching emission reduction targets. Comparison with other countries highlights both the magnitude of the problem in China and the substantial opportunities for improvement. This research directly addresses the urgent need for national-level policies to mitigate agricultural ammonia emissions in China. The framework and findings provide valuable information for policy makers in establishing effective strategies and targets. While the study acknowledges limitations, it offers a comprehensive, quantitative assessment, laying the groundwork for more nuanced future research.

This study provides a comprehensive quantitative assessment of the societal benefits and abatement costs of reducing agricultural ammonia emissions in China. The findings strongly support the implementation of a coordinated mitigation strategy that includes both technical (improved fertilizer and manure management, improved animal housing) and non-technical (dietary changes) measures. Prioritizing cost-effective options such as reducing urea-based fertilizer and protein-rich animal feed can achieve substantial emission reductions at minimal or even negative costs, providing a strong foundation for subsequent, more expensive measures. Future research could focus on regional-level analyses to account for variations in agricultural practices and environmental conditions, and explore the full range of interactions between ammonia mitigation and other environmental concerns, such as the effect on soil health and biodiversity.

The study acknowledges several limitations: The cost-benefit analysis did not fully incorporate the effects of NH3 mitigation on crop yields or animal productivity due to data limitations. Regional differences in agricultural structures and environmental conditions were not explicitly addressed. The climate benefits were limited to non-CO2 greenhouse gas emissions. Complex chemical interactions between SO2, NOx, and NH3 in the atmosphere were not fully accounted for. The projections for 2050 are based on current technologies and may change with future technological advancements. Despite these limitations, the study provides a valuable initial assessment, forming a basis for future refinements.