Combing GOME-2B and OMI Satellite Data to Estimate Near-Surface NO2 of Mainland China

Near-surface NO 2 (NS-NO 2 ) is closely related to human health and the atmospheric environment. While top-down approaches have been widely applied to estimate NS-NO 2 using satellite-based NO 2 column measurements, there still exist significant defects, resulting in a low overall fit and significant amount of bias. This article combines GOME-2B and OMI satellite data to estimate daily NS-NO 2 with a spatial resolution of 0.1° × 0.1° from 2014 to 2018 over Mainland China, using a machine learning method. The estimated result has four important characteristics. First, the sample-based cross validation with surface observations shows a good result with R 2 = 0.80 and RMSE = 9.0 μ g/m 3 . Second, the underestimation in high concentration areas and overestimation in low concentration areas are both reduced, compared with the case of using OMI data alone. Third, the estimated NS-NO 2 is consistent with surface observations in spatial distribution, and successfully represent both inter-annual changes and seasonal characteristics. Furthermore, the population-weighted NO 2 -based estimated dataset shows a significant decline of pollution exposure levels from 2014 to 2018.