Enhanced atmospheric ammonia (NH3) pollution in China from 2008 to 2016: Evidence from a combination of observations and emissions.

The increase of gaseous ammonia (NH3) 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 NH3 (the ANNI-NH3-v2.1R-I, hereafter referred to as IASI_NH3_R) and to analyze the spatial and temporal characteristics of atmospheric NH3 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 NH3 concentrations and the measured near-ground NH3 measurements over different land covers in Eastern China, suggesting the IASI_NH3_R product can be used to investigate spatial and temporal trends of atmospheric NH3 concentration. The annual mean NH3 column concentrations peaked in the North China Plain (averaged 12 × 1015 mol cm-2 yr-1) and showed a significant increasing trend at a rate of 0.6 × 1015 mol cm-2 yr-1 during the entire period, which can be ascribed to densely populated, intensive agricultural activities and substantial reduction of SO2 and NO2 emissions since 2011. The NH3 column concentrations show a slight increase in winter in most regions of China, probably due to less precipitation amount and increased uncertainty for lower NH3 columns and the thermal contrast (TC). A large seasonal variation of NH3 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 NH3 emissions and meteorological conditions. Our results suggest that the current control measures effectively decreased SO2 and NO2 pollution but are not yet apparent in the mitigation of atmospheric NH3 pollution, which also merits more attention considering that no effective measures are being implemented for NH3 emission control at a regional or national scale in China.