Enhanced atmospheric ammonia (NH) pollution in China from 2008 to 2016: Evidence from a combination of observations and emissions.

The increase of gaseous ammonia (NH) concentration in the atmosphere significantly impacts the regional air quality, human health, and the nitrogen cycle of ecosystems. This study aims to verify the reanalyzed product of IASI NH (the ANNI-NH-v2.1R-I, hereafter referred to as IASI_NH_R) and to analyze the spatial and temporal characteristics of atmospheric NH during 2008-2016 and its underlying influencing factors. Our results show a good agreement between spatial pattern and temporal (annual and monthly) trend of the satellite-derived surface NH concentrations and the measured near-ground NH measurements over different land covers in Eastern China, suggesting the IASI_NH_R product can be used to investigate spatial and temporal trends of atmospheric NH concentration. The annual mean NH column concentrations peaked in the North China Plain (averaged 12 × 10 mol cm yr) and showed a significant increasing trend at a rate of 0.6 × 10 mol cm yr during the entire period, which can be ascribed to densely populated, intensive agricultural activities and substantial reduction of SO and NO emissions since 2011. The NH column concentrations show a slight increase in winter in most regions of China, probably due to less precipitation amount and increased uncertainty for lower NH columns and the thermal contrast (TC). A large seasonal variation of NH column concentrations was observed, with the highest values in summer and the lowest in autumn. Such seasonal variation is mainly affected by seasonal differences in NH emissions and meteorological conditions. Our results suggest that the current control measures effectively decreased SO and NO pollution but are not yet apparent in the mitigation of atmospheric NH pollution, which also merits more attention considering that no effective measures are being implemented for NH emission control at a regional or national scale in China.