Numerical analysis of agricultural emissions impacts on PM_2.5 in China using a high-resolution ammonia emission inventory

Abstract

Abstract. China is one of the largest agricultural countries in the world. Thus, NH3 emission from agricultural activities in China considerably affects the country's regional air quality and visibility. In this study, a high-resolution agricultural NH3 emission inventory compiled on 1 km × 1 km horizontal resolution was applied to calculate the NH3 mass burden in China and reliably estimate the influence of NH3 on agriculture. The key parameter emission factors of this inventory were enhanced by considering many experiment results, and the dynamic data of spatial and temporal information were updated using statistical data of 2015. In addition to fertilizers and husbandry, farmland ecosystems, livestock waste, crop residue burning, wood-based fuel combustion, and other NH3 emission sources were included in this inventory. Furthermore, a source apportionment tool, namely, the Integrated Source Apportionment Method (ISAM) coupled with the air quality modeling system Regional Atmospheric Modeling System and Community Multiscale Air Quality, was applied to capture the contribution of NH3 emitted from total agriculture (Tagr) in China. The aerosol mass concentration in 2015 was simulated, and results showed that the high mass concentration of NH3 exceeded 10 µg m−3 and mainly appeared in the North China Plain, Central China, the Yangtze River Delta, and the Sichuan Basin. Moreover, the annual average contribution of Tagr NH3 to PM2.5 mass burden was 14 %–22 % in China. Specific to the PM2.5 components, Tagr NH3 contributed dominantly to ammonium formation (87.6 %) but trivially to sulfate formation (2.2 %). In addition, several brute-force sensitivity tests were conducted to estimate the impact of Tagr NH3 emission reduction on PM2.5 mass burden. In contrast to the result of ISAM, even though the Tagr NH3 only provided 10.1 % contribution to nitrate under the current emission scenario, the reduction of nitrate could reach 95.8 % upon removal of the Tagr NH3 emission. This deviation occurred because the contribution of NH3 to nitrate should be small under a “rich NH3”environment and large under a “poor NH3” environment. Thus, the influence of NH3 on nitrate formation would be enhanced with the decrease in ambient NH3 mass concentration.