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Limited availability of atmospheric ammonia (NH3) 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 NH3 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 NH3 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 NH3 in Asia, both using the model and satellite observations. In general, a close agreement was found between yearly averaged NH3 total columns simulated by the model and IASI satellite measurements over the IGP, South Asia (r=0.81), and the North China Plain (NCP), East Asia (r=0.90). However, the MOZART-4-simulated NH3 column was substantially higher over South Asia than East Asia, as compared with the IASI retrievals, which show smaller differences. Model-simulated surface NH3 concentrations indicated smaller concentrations in all seasons than surface NH3 measured by the ground-based observations over South and East Asia, although uncertainties remain in the available surface NH3 measurements. Overall, the comparison of East Asia and South Asia using both MOZART-4 model and satellite observations showed smaller NH3 columns in East Asia compared with South Asia for comparable emissions, indicating rapid dissipation of NH3 due to seconda

Limited availability of atmospheric ammonia (NH3)observations limits our understanding of controls on its spatial andtemporal variability and its interactions with the ecosystem. Here we used theModel for Ozone and Related chemical Tracers version 4 (MOZART-4) global chemistrytransport model and the Hemispheric Transport of Air Pollution version 2(HTAP-v2) emission inventory to simulate global NH3 distribution forthe year 2010. We presented a first comparison of the model with monthlyaveraged satellite distributions and limited ground-based observationsavailable across South Asia. The MOZART-4 simulations over South Asia andEast Asia were evaluated with the NH3 retrievals obtained from theInfrared 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 MonitoringNetwork (NNDMN) of China. We identified the northern region of India(Indo-Gangetic Plain, IGP) as a hotspot for NH3 in Asia, both usingthe model and satellite observations. In general, a close agreement wasfound between yearly averaged NH3 total columns simulated by the modeland IASI satellite measurements over the IGP, South Asia (r=0.81), andthe North China Plain (NCP), East Asia (r=0.90). However, the MOZART-4-simulated NH3 column was substantially higher over South Asia thanEast Asia, as compared with the IASI retrievals, which show smallerdifferences. Model-simulated surface NH3 concentrations indicatedsmaller concentrations in all seasons than surface NH3 measured bythe ground-based observations over South and East Asia, althoughuncertainties remain in the available surface NH3 measurements.Overall, the comparison of East Asia and South Asia using both MOZART-4model and satellite observations showed smaller NH3 columns in EastAsia compared with South Asia for comparable emissions, indicating rapiddissipation of NH3 due to secondary aerosol form, SCOPUS: ar.j, info:eu-repo/semantics/published