Analysis of atmospheric ammonia over South and East Asia based on the MOZART-4 model and its comparison with satellite and surface observations

Abstract

Limited availability of atmospheric ammonia (NHspan classCombining double low line"inline-formula"3/span) observations limits our understanding of controls on its spatial and temporal variability and its interactions with the ecosystem. Here we used the Model for Ozone and Related chemical Tracers version 4 (MOZART-4) global chemistry transport model and the Hemispheric Transport of Air Pollution version 2 (HTAP-v2) emission inventory to simulate global NHspan classCombining double low line"inline-formula"3/span distribution for the year 2010. We presented a first comparison of the model with monthly averaged satellite distributions and limited ground-based observations available across South Asia. The MOZART-4 simulations over South Asia and East Asia were evaluated with the NHspan classCombining double low line"inline-formula"3/span retrievals obtained from the Infrared Atmospheric Sounding Interferometer (IASI) satellite and 69 ground-based monitoring stations for air quality across South Asia and 32 ground-based monitoring stations from the Nationwide Nitrogen Deposition Monitoring Network (NNDMN) of China. We identified the northern region of India (Indo-Gangetic Plain, IGP) as a hotspot for NHspan classCombining double low line"inline-formula"3/span in Asia, both using the model and satellite observations. In general, a close agreement was found between yearly averaged NHspan classCombining double low line"inline-formula"3/span total columns simulated by the model and IASI satellite measurements over the IGP, South Asia (span classCombining double low line"inline-formula"ir/iCombining double low line0.81/span), and the North China Plain (NCP), East Asia (span classCombining double low line"inline-formula"ir/iCombining double low line0.90/span). However, the MOZART-4-simulated NHspan classCombining double low line"inline-formula"3/span column was substantially higher over South Asia than East Asia, as compared with the IASI retrievals, which show smaller differences. Model-simulated surface NHspan classCombining double low line"inline-formula"3/span concentrations indicated smaller concentrations in all seasons than surface NHspan classCombining double low line"inline-formula"3/span measured by the ground-based observations over South and East Asia, although uncertainties remain in the available surface NHspan classCombining double low line"inline-formula"3/span measurements. Overall, the comparison of East Asia and South Asia using both MOZART-4 model and satellite observations showed smaller NHspan classCombining double low line"inline-formula"3/span columns in East Asia compared with South Asia for comparable emissions, indicating rapid dissipation of NHspan classCombining double low line"inline-formula"3/span due to secondary aerosol formation, which can be explained by larger emissions of acidic precursor gases in East Asia./.