Surface NO 2 volume mixing ratio (VMR) at a specific time (13:45 Local time) (NO 2 VMR ST ) and monthly mean surface NO 2 VMR (NO 2 VMR M ) are estimated for the first time using three regression models with Ozone Monitoring Instrument (OMI) data in four metropolitan cities in South Korea: Seoul, Gyeonggi, Daejeon, and Gwangju. Relationships between the surface NO 2 VMR obtained from in situ measurements (NO 2 VMR In-situ ) and tropospheric NO 2 vertical column density obtained from OMI from

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... 7 to 2013 were developed using regression models that also include boundary layer height (BLH) from Atmospheric Infrared Sounder (AIRS) and surface pressure, temperature, dew point, and wind speed and direction. The performance of the regression models is evaluated via comparison with the NO 2 VMR In-situ for two validation years (2006 and 2014). Of the three regression models, a multiple regression model shows the best performance in estimating NO 2 VMR ST and NO 2 VMR M . In the validation period, the average correlation coefficient (R), slope, mean bias (MB), mean absolute error (MAE), root mean square error (RMSE), and percent difference between NO 2 VMR In-situ and NO 2 VMR ST estimated by the multiple regression model are 0.66, 0.41, −1.36 ppbv, 6.89 ppbv, 8.98 ppbv, and 31.50%, respectively, while the average corresponding values for the other two models are 0.75, 0.41, −1.40 ppbv, 3.59 ppbv, 4.72 ppbv, and 16.59%, respectively. All three models have similar performance for NO 2 VMR M , with average R, slope, MB, MAE, RMSE, and percent difference between NO 2 VMR In-situ and NO 2 VMR M of 0.74, 0.49, −1.90 ppbv, 3.93 ppbv, 5.05 ppbv, and 18.76%, respectively.