SATELLITE OBSERVATIONS OF TROPOSPHERIC NO₂ OVER ASIA: ANALYSIS OF SEASONAL VARIATIONS AND COMPARISON WITH MODEL

Abstract

 Long-term trends of tropospheric NO₂ columns from four satellites, GOME, SCIAMACHY, OMI and GOME-2, are analyzed over the capital cities in Southeast Asia, Japan and China for the period 1996 to 2011. The results show a significant increase in tropospheric NO₂ columns over Shanghai during the study period (21.5% yr^-1, reference year 1996). The seasonal variability reveals a different pattern between the different city locations. The cities located in low- and mid- latitude show the maximum levels in wintertime and minimum in summertime. Reversely, those cities near Equator give the opposite results. The inter-comparisons between the satellites show reasonably well agreements with the correlations larger than 0.75. The consistency between NO_x emissions from several regional and global emission inventories and tropospheric NO₂ columns is investigated and give the different results for each city due to the effect of meteorology. The comparison of ground- and satellite-based NO₂ are performed for several stations. The results illustrate better relations for OMI and GOME-2 than GOME and SCIAMACHY owing to the differences in satellite overpass time and spatial resolutions. Finally, the results of seasonal variability from GEOS-Chem simulation generally agree well with satellite measurements. However, the model underestimated retrieved tropospheric NO₂ columns by the factor of 3-4.