Highly resolved global distribution of tropospheric NO₂ using GOME narrow swath mode data

Abstract

Abstract. The Global Ozone Monitoring Experiment (GOME, since 1995) allows the retrieval of global total column densities of atmospheric trace gases, including NO2. Tropospheric vertical column densities (VCDs) are derived by estimating the stratospheric fraction from measurements over the remote ocean. Mean maps of tropospheric NO2 VCDs derived from GOME clearly allow to detect regions with enhanced industrial activity, but the standard spatial resolution of the GOME ground pixels (320×40 km2) is insufficient to resolve regional trace gas distributions or individual cities. Within the nominal GOME operation, every tenth day measurements in the so called narrow swath mode are executed with a much better spatial resolution (80×40 km2). Though the global coverage of these data is – due to the narrow swath – rather poor, the mean distribution over several years (1997–2001) allows to construct a much more detailed picture of the global NO2 distribution, especially if corrected for seasonal effects. It vividly illustrates the shortcomings of the standard size GOME pixels and reveals an unprecedented wealth of details in the global distribution of tropospheric NO2. Sharply localised spots of enhanced NO2 VCD can be associated directly to cities, large power plants, and heavy industry centers. The long time series of GOME data allows a quantitative comparison of the narrow swath mode data to the nominal resolution that holds general information on the dependency of NO2 VCDs on pixel size. This is important for new instruments like SCIAMACHY (launched March 2002 on ENVISAT) or OMI and GOME II (to be launched 2004 and 2005, respectively) with an improved spatial resolution.