High-resolution ammonia emission inventories with comprehensive analysis and evaluation in Henan, China, 2006–2016

Henan province is one of the most critical emitters of ammonia (NH3) and is one of the most seriously air polluted regions in China. In this study, we developed a first comprehensive and novel 2015-based NH3 emission inventory for Henan province based on investigational activity data with corrected and updated emission factors of anthropogenic and natural sources. The 3 km × 3 km gridded emissions and monthly variations were allocated by using appropriate spatial and localized temporal surrogates. The total NH3 emission was 1031.6 Gg in 2015, of which livestock, N fertilizer application, and humans were the top three contributors, accounting for 57.3%, 28.2%, and 3.1%, respectively. The cities of Nanyang, Zhoukou, and Zhumadian with more rural and agricultural activities were demonstrated to have relatively high emissions, accounting for 12.5%, 10.1%, and 9.7% of total emissions, respectively. The regional averaged emission density was 6.3 t km−2, with higher values in eastern and northern Henan province. Obvious seasonal variability was observed, with the highest emission in July and the lowest in January associated with temperature and local farming activities. In addition, according to the emissions investigation carried out from 2006 to 2016, the largest changes occurred in non-agricultural sources. Furthermore, we quantitatively analyzed the estimated emissions with the uncertainty range of -33%-35% using the AuvToolPro tool. This emission inventory was also evaluated by comparing the magnitudes with other studies, analyzing the correlation of the observed ambient NH3 concentration with emission density and temperature, and investigating the trend of molar ratio of (2SO2+NO2)/NH3. The emission inventory developed in this study can provide information to understand local emission characteristics, and to determine how to prioritize effective control strategies properly for policy makers.