Downward trend of NO2 in the urban areas of Beijing-Tianjin-Hebei region from 2014 to 2020: Comparison of satellite retrievals, ground observations, and emission inventories

Significant downward trend of NO2 over BTH region has been detected by both satellite and ground surface observations in recent years due to the continuous regulatory policies in China. Previous studies mostly focused on the scientific issue of analyzing the distribution characteristics of NO2 and the drivers of interannual NO2 variations. Whether the declines derived from independent data sets with different spatiotemporal representations are comparable? If they are, what is the significance of these observed quantitative interannual trends for evaluating the estimated NOx emission changes is poorly characterized. This issue is still need to be brought to more attention.