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Sulphur dioxide plumes detection from Sentinel-5P TROPOMI

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Emission of SO2 can have an important impact on air quality and climate, as well as pose a threat to aircraft in case of injection into the upper atmosphere after volcanic eruptions. The “UV-visible observations” group is developing new algorithms for the high-resolution Sentinel-5P TROPOMI instrument which enables to determine the SO2 column and height with unprecedented level of details and sensitivity.
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Sulphur dioxide (SO2) is emitted into the Earth’s atmosphere through human activities, from coal-burning powerplants, oil and gas industry, smelters, and through natural processes, mostly from volcanoes.

To monitor and estimate global atmospheric SO2 emissions, accurate and sensitive detection from space is highly important. Traditionally the detection of SO2 in the UV is achieved using the Differential Optical Absorption Spectroscopy (DOAS) technique. However, this method is typically accompanied by substantial biases and high levels of noise in the retrieved SO2 data.

Alternative algorithm for the retrieval of SO2 columns

The UV-visible observations group of BIRA-IASB has developed an alternative algorithm for the retrieval of SO2 columns from satellite observations. The validity of this approach, named COBRA, was demonstrated on measurements from the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor (S-5P) satellite.

The method significantly reduces both the noise and biases present in the current TROPOMI operational SO2 retrievals. In the future, COBRA will be implemented in the TROPOMI operational SO2 processor.

Our SO2 signal map (full-screen version, with additional options) shows the global S-5P/TROPOMI SO2 signal, averaged over two and a half years (May 2018 - December 2020). Much of the biases and areas of false SO2 detection seen in previous data versions, are largely solved with COBRA. Zooming in over polluted regions even reveals new weak SO2 sources.

Recently, the concept of COBRA has also been expanded successfully to the determination of volcanic SO2 plume height. This information is of great value for the mitigation of volcanic risks to aviation and for better quantifying volcanic SO2 emissions. 



  • Theys, N., Fioletov, V., Li, C., De Smedt, I., Lerot, C., McLinden, C., Krotkov, N., Griffin, D., Clarisse, L., Hedelt, P., Loyola, D., Wagner, T., Kumar, V., Innes, A., Ribas, R., Hendrick, F., Vlietinck, J., Brenot, H., Van Roozendael, M. A sulfur dioxide Covariance-Based Retrieval Algorithm (COBRA): application to TROPOMI reveals new emission sources, Atmospheric Chemistry and Physics, Vol: 21, issue: 22, 16727-16744, DOI: 10.5194/acp-21-16727-2021, 2021
  • Theys, N., Lerot, C., Brenot, H., Van Gent, J., De Smedt, I., Clarisse, L., Burton, M., Varnam, M., Hayer, C. Esse, B., Van Roozendael, M. Improved retrieval of SO2 plume height from TROPOMI using an iterative Covariance-Based Retrieval Algorithm, Atmospheric Measurement Techniques, Vol: 15, issue: 16, 4801-4817, DOI: 10.5194/amt-15-4801-2022, 2022
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Figure 2 caption (legend)
Map of S-5P/TROPOMI SO2 vertical column, averaged over a 2.5 year period. Consult the full-screen version of the map, with additional options via the link in the text.
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