Numerical analysis of the impact of agricultural emissions on PM2.5 in China using a high-resolution ammonia emissions inventory.

China is one of the largest agricultural countries in the world. The NH₃ emissions from agricultural activities in China significantly affect regional air quality and horizontal visibility. To reliably estimate the influence of NH₃ on agriculture, a high-resolution agricultural NH₃ emissions inventory, compiled with a 1 km x 1 km horizontal resolution, was applied to calculate the NH₃ mass burden in China. The key emission factors of this inventory were enhanced by considering the results of many native experiments, and the activity data of spatial and temporal information were updated using statistical data from 2015. Fertilizer and husbandry, as well as farmland ecosystems, livestock waste, crop residue burning, fuel wood combustion, and other NH₃ emission sources were included in the inventory. Furthermore, a source apportionment tool, ISAM (Integrated Source Apportionment Method), coupled with the air quality modeling system RAMS-CMAQ (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 the results showed that a high mass concentration of NH₃, which exceeded 10 µg m^-3, appeared mainly in the North China Plain (NCP), Central China (CNC), the Yangtz River Delta (YRD), and the Sichan Basin (SCB), and the annual average contribution of Tagr NH₃ to PM_2.5 mass burden in China was 14-18 %. Specific to the PM_2.5 components, Tagr NH₃ provided a major contribution to ammonium formation (87.6 %) but a tiny contribution to sulfate (2.2 %). In addition, several brute-force sensitivity tests were conducted to estimate the impact of Tagr NH₃ emissions reduction on the PM_2.5 mass burden. Compared with the results of ISAM, it was found that even though the Tagr NH₃ only contributed 10.1 % of nitrate under current emissions scenarios, the reduction of nitrate could reach 98.8 % upon removal of the Tagr NH₃ emissions. The main reason for this deviation could be that the NH₃ contribution to nitrate is small under "rich NH₃" conditions and large in "poor NH₃" environments. Thus, the influence of NH₃ on nitrate formation could be enhanced with the decrease of ambient NH₃ mass concentration. [ABSTRACT FROM AUTHOR]