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Sulphur Dioxide SO2

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Sulphur Dioxide – SO2

SO2 is another pollutant leaving a clear absorption signature in SCIAMACHY spectra. Sources of SO2 are combustion of sulphur rich coal and other fossil fuels or volcanic eruptions including degassing. Although SO2 emissions have been reduced significantly over the last decades, clear signals can be detected over the Eastern US and, in particular, the polluted areas of China (fig. 3-8). As in the case of NO2, the high spatial resolution facilitates source identification and makes the dataset an interesting new data source for air pollution research. By combining GOME and SCIAMACHY results, the long-term trend of SO2 emissions in heavily polluted areas can be inferred and compared with similar analyses for NO2 (see inset of fig. 3-8).


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fig. 3-8

Average SO2 vertical column densities (VCD) over eastern China during the year 2003. SCIAMACHY's improved spatial resolution permits to identify localised emissions due to anthropogenic activities. The trend analysis uses data from GOME (1996-2002) and SCIAMACHY (2003-2009). (Graphics: map - M. Van Roozendael, BIRA-IASB; trend - A. Richter, IUP-IFE, University of Bremen)

Volcanoes are a natural source of SO2. Since the start of SCIAMACHY’s routine observations, a few of the several hundred existing active volcanoes have been erupting and were overpassed by ENVISAT. In October 2002, Mt. Etna on the island of Sicily entered an explosive phase. The rectangular overlay in fig. 3-9 represents a SCIAMACHY nadir measurement displaying SO2 emissions which match well with the ash plume visible on an image simultaneously obtained by MERIS on ENVISAT. The SO2 emissions of volcanic eruptions are usually associated with such volcanic ash plumes. These could be a major threat for air traffic. Therefore, SCIAMACHY SO2 retrievals are used in early warning services in support of aviation control. Whenever elevated SO2 densities are obtained in regions with known volcanoes, an alert is issued indicating a potential volcanic ash cloud.


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fig. 3-9

The Mt. Etna volcanic eruption in 2002 with obvious SO2 emissions (reddish plume). The SCIAMACHY nadir measurement is overlayed on a MERIS image showing that the plume of SO2 and the visible ash cloud match well. (Graphics: ESA and Brockmann Consult)


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