Abstract

Surface NO2 volume mixing ratio (VMR) at a specific time (13:45 Local time) (NO2 VMRST) and monthly mean surface NO2 VMR (NO2 VMRM) 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 NO2 VMR obtained from in situ measurements (NO2 VMRIn-situ) and tropospheric NO2 vertical column density obtained from OMI from 2007 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 NO2 VMRIn-situ for two validation years (2006 and 2014). Of the three regression models, a multiple regression model shows the best performance in estimating NO2 VMRST and NO2 VMRM. 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 NO2 VMRIn-situ and NO2 VMRST 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 NO2 VMRM, with average R, slope, MB, MAE, RMSE, and percent difference between NO2 VMRIn-situ and NO2 VMRM of 0.74, 0.49, −1.90 ppbv, 3.93 ppbv, 5.05 ppbv, and 18.76%, respectively.

Highlights

  • The main anthropogenic source of nitrogen dioxide (NO2 ) is fossil fuel combustion, while natural sources of NO2 include lightning, forest fires, and soil emissions [1,2]

  • A slightly larger difference in magnitude is found between NO2 VMRIn-situ and NO2 VMRST obtained with M3 compared to those between NO2 VMRIn-situ and NO2 VMRST obtained with M1 and M2

  • Monthly and specific time estimates of NO2 volume mixing ratio (VMR) were obtained for the first time using three regression models in four metropolitan cities for two years, 2006 and 2014

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Summary

Introduction

The main anthropogenic source of nitrogen dioxide (NO2 ) is fossil fuel combustion, while natural sources of NO2 include lightning, forest fires, and soil emissions [1,2]. In terms of its effect on human health, long-term NO2 exposure can lead to respiratory depression and respiratory illness [4,5,6,7,8]. It is a precursor of aerosol nitrate, tropospheric ozone, and the hydroxyl radical (OH), the main atmospheric oxidant [9]. It is important to measure NO2 and various methods are used, with chemiluminescence, a well-known technique for measuring surface NO2 volume mixing ratio (VMR) [10]. In situ measurements such as Remote Sens. 2017, 9, 627; doi:10.3390/rs9060627 www.mdpi.com/journal/remotesensing

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