Trends and Spatiotemporal Patterns of Tropospheric NO2 over China During 2005-2014

Nitrogen dioxide (NO2) is one of the major atmospheric pollutants, and the concentration of NO2 is regarded as one of the indicators of air quality. In the past decades, China has experienced rapid economic growth and severe NO2 pollution to match. We evaluate the trends and spatiotemporal patterns of tropospheric NO2 over mainland China from 2005 to 2014 using vertical column density (VCD) datasets retrieved from the Ozone Monitoring Instrument (OMI). Results show that from 2005 to 2014, NO2 pollution regions have enlarged at the national scale, and high NO2 VCDs are mainly concentrated over highly populated regions in eastern China. The year 2011 is the turning point. Tropospheric NO2 VCDs first significantly increase by 0.19 x 10(15) molec cm(-2) year(-1) (R-2 = 0.94, P = 0.002) from 2005 to 2011, and then decrease by 0.21 x 10(15) molec cm(-2) year(-1) (R-2 = 0.97, P = 0.016) from 2011 to 2014. Since 2011, tropospheric NO2 VCDs over central-east China decrease remarkably. Tropospheric NO2 VCDs is higher in November (3.630 x 10(15) molec/cm(2)), December (4.758 x 10(15) molec/cm(2)), and January (4.863 x 10(15) molec/cm(2)), while lower in July (1.684 x 10(15) molec/cm(2)), August (1.627 x 10(15) molec/cm(2)), and September (1.703 x 10(15) molec/cm(2)), indicating that winter and spring are the most polluted seasons. Due to the huge gap in population density and industry development between western and eastern China, the spatial pattern of tropospheric NO2 VCDs shows large west-east difference.