Variations of the increasing trend of tropospheric NO2 over central east China during the past decade

A numerical analysis using a regional chemical transport model (CTM) is presented in comparison with Global Ozone Monitoring Experiment (GOME) and SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) satellite NO2 measurements over East Asia from 1996 to 2005 from a climatological perspective. Modeling results agree well with satellite retrievals in geographical distribution patterns, with systematic underestimation of the absolute values. The sharp increase in NO2 vertical column densities (VCDs) over central east China (CEC) after the year 2000 (14.1–20.5% yr−1 for the satellite observations and 10.8% yr−1 for model simulations) is analyzed quantitatively over different megacity clusters. The distinct emission increase patterns are responsible for the different increase trends observed over the Beijing megacity cluster (BJ), the Yangtze Delta (YD) and other CEC regions. The growth rate of satellite measured and CMAQ-modeled NO2 VCDs for the YD is much higher than that in other regions, with no clear seasonal variation. Apart from BJ and YD, NO2 emissions from other regions in CEC also expand considerably.