Summary: | Fine-scale nitrogen oxide (NO<sub>x</sub>) concentrations over South Korea are examined using surface observations, satellite data and high-resolution model simulations based on the latest emission inventory. While accurate information on NO<sub>x</sub> emissions in South Korea is crucial to understanding regional air quality in the region, consensus on the validation of NO<sub>x</sub> emissions is lacking. We investigate the spatial and temporal variation in fine-scale NO<sub>x</sub> emission sources over South Korea. Surface observations and newly available fine-scale satellite data (TROPOspheric Monitoring Instrument; TROPOMI; 3.5 × 7 km<sup>2</sup>) are compared with the community multiscale air quality (CMAQ) model based on the clean air policy support system (CAPSS) 2016 emission inventory. The results show that the TROPOMI NO<sub>2</sub> column densities agree well with the CMAQ simulations based on CAPSS emissions (e.g., R = 0.96 for June 2018). The surface observations, satellite data and model are consistent in terms of their spatial distribution, the overestimation over the Seoul Metropolitan Area and major point sources; however, the model tends to underestimate the surface concentrations during the cold season.
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