Reconstruction of Non-agricultural Ammonia Emission Inventory Based on Isotopic Source Apportionment in China

Isotopic source apportionment results revealed that non-agricultural sectors are a significant source of ammonia (NH₃) emissions, particularly in urban areas. Unfortunately, non-agricultural sources have been substantially underrepresented in the current anthropogenic NH₃ emission inventories (EIs). Therefore, based on the isotopic source apportionment results and the emission ratios of carbon monoxide (CO) and NH₃, this study reconstructed a gridded EI of non-agricultural NH₃ in China for the year 2016. The isotope-corrected non-agricultural NH₃ emissions in China were estimated to be 4370 Gg, with the contribution of non-agricultural sectors increasing from 7% to 31%. Spatially, high amounts of non-agricultural NH₃ emissions were mainly concentrated in China's highly urbanized and densely inhabited regions. More importantly, according to simulation from the WRF-Chem model driven by the isotope-corrected NH₃ EI compared to the original NH₃ EI, the average biases for the surface concentrations and dry deposition flux of reduced nitrogen (NH_x = gaseous NH₃ + particulate NH₄⁺) have decreased by 23% and 31%, respectively. Overall, this study develops a preliminary and sound estimate of previously underestimated non-agricultural NH₃ emissions and offers a comprehensive and accurate NH₃ EI for the efficient prevention and control of air pollution in China.