Agricultural ammonia emissions and its impact on PM2.5 concentrations in the Beijing–Tianjin–Hebei region from 2000 to 2018

Ammonia (NH3) discharged from agricultural activities to the atmosphere plays a crucial role in the formation of secondary inorganic aerosols. This study analyzed the temporal-spatial development of agricultural NH3 emissions from 2000 to 2018 in the Beijing-Tianjin-Hebei (BTH) region and assessed the effects of reducing PM2.5 by removing agricultural NH3 using an air quality model. The results showed that the interannual agricultural NH3 emissions in the BTH region exhibited a stairs trend from 2000 to 2018, with an average of 971.63 Gg. In particular, agricultural NH3 emissions in the BTH region reached a maximum in summer when the temperature was high and were more concentrated in the southern plains compared to the northern areas. Under the reduction scenario (RS), the agricultural NH3 emissions in the BTH region in 2015, 2016, 2017, and 2018 were reduced by 2.95%, 4.10%, 18.75%, and 10.21%, resulting in a reduction of 0.5%, 0.5%, 2.5%, and 1.2% of annual mean PM2.5 concentration, respectively, compared with the baseline scenario (BS). Furthermore, agricultural NH3 emissions contributed 12.6, 12.1, 11.9, and 11.3 μg m-3 to PM2.5 concentrations in 2015, 2016, 2017, and 2018 under the zero-emission scenario (ZS), respectively. However, the contribution rates exhibited a slightly increasing trend from 20.5% in 2015 to 24.6% in 2018. These findings could provide a new understanding of agricultural NH3 emission trends and their impacts on PM2.5 concentration based on actual NH3 mitigation ratios in recent years, thereby guiding the formulation of future control strategies.