Providing information on sulphur dioxide from the Cumbre Vieja eruption to aviation.

For the first time since 1971, the Cumbre Vieja volcano on La Palma (Canary Islands, Spain) started to erupt on 19 September 2021 at 13:10 UTC, more than a month ago. Together with the outflowing lava, the volcano emits ash and several gases, amongst these sulphur dioxide (SO2). Volcanic ash and SO2 are dangerous to public health and aviation (damage to engine due to ash melting and sulphidation). Therefore, tracking and monitoring volcanic plumes and their constituents is very important. For this reason, since 2009 the Support to Aviation Control Service (SACS; system uses satellite observations from UV-vis and IR hyperspectral sensors to detect ash and SO2 emissions. For this particular eruption, no ash notification has currently been sent by SACS. However, since the start of the eruption, daily notifications of exceptional SO2 concentrations have been sent to users by the SACS system. Dedicated webpages are created with key information and links to tailored images (e.g., alert and Google Earth) and data (e.g., In particular, the alert data file available through the SACS notifications are referred as NCAP, for NetCDF Alert Products (see details in Brenot et al. 2014, 2021).

A key source of information in the context of the Cumbre Vieja eruption comes from the Tropospheric Ozone Monitoring Instrument (TROPOMI) onboard the Copernicus Sentinel-5P satellite. TROPOMI provides observations at an unprecedented 3.5 × 5.5 km2 spatial resolution and BIRA-IASB is in charge of the algorithm development to retrieve SO2 columns from TROPOMI (Theys et al., 2017, 2019). SACS/ALARM EWS observes SO2 with other sensors, such as the Infrared Atmospheric Sounding Interferometer (IASI) onboard the MetOp satellites and the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard the geosynchronous Meteosat Second generation satellites.

The transport of the SO2 plume as observed by TROPOMI and SEVIRI instruments over northern Africa, southern Europe and the Atlantic Ocean from the 19th of September to the 20th of October 2021, is shown in the animation below. The right panel shows the RGB Ash composite product from EUMETSAT. This product has a high temporal resolution and allows to follow and nowcast the transport of the plume. However, the SO2 detection from this broadband instrument is limited, as can be seen when comparing to the daily observations of TROPOMI SO2 vertical column density (left panel).

TROPOMI SO2 vertical column density (left) and SO2 mass (upper left time-series), and SEVIRI RGB composite Ash (right). The Cumbre Vieja location is indicated in the left and right panels respectively, by the black and the red triangles. The various RGB interpretations are indicated to the right. SO2 maxima (in Dobson Units) and time tags are shown in the TROPOMI images. The mean overpass time of TROPOMI sensor over Canary Islands is about 15:00 UTC.

The animation shows that the emitted SO2 has been transported from the surroundings of the Canary Islands to the North of Africa (e.g., on 27 Sept. and 9 Oct.), to the South of Europe (e.g., on 25-26 Sept. and 19-20 Oct.), and along the Atlantic Ocean (e.g., on 30 Sept. and 6 Oct.). From the 19th October onwards the plume was transported towards Portugal, Spain, France, UK and the Benelux. The observations on 20 October show a horizontal very thin plume of few hundred kilometers wide (an atmospheric river) which brings SO2 towards Germany, Switzerland, Italy and Poland. This animation shows the added value of combining complementary observations from different satellite platforms, using different spectral information and different temporal resolutions.

For the time being, it is plausible that the eruption will continue for several weeks or even months. The volcanic emissions of Cumbre Vieja have not stopped since one month with ~50 kt of SO2 emitted per day (inset figure of left panel) and a total of ~1.5 Tg.

Acknowledgements: We thank Pierre de Buyl and Nicolas Clerbaux from the Royal Meteorological Institute of Belgium (IRM-KMI) for providing near real-time access to SEVIRI data used in the frame of ALARM H2020 project ( We are currently working on the development and the implementation in SACS of selective detection of SO2 and aerosols (Ash and dust) from SEVIRI.

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Brenot, H., Theys, N., Clarisse, L., van Geffen, J., van Gent, J., Van Roozendael, M., van der A, R., Hurtmans, D., Coheur, P.-F., Clerbaux, C., Valks, P., Hedelt, P., Prata, F., Rasson, O., Sievers, K., and Zehner, C.: Support to Aviation Control Service (SACS): an online service for near-real-time satellite monitoring of volcanic plumes, Nat. Hazards Earth Syst. Sci., 14, 1099–1123 (2014).

Brenot, H., Theys, N., Clarisse, L., van Gent, J., Hurtmans, D. R., Vandenbussche, S., Papagiannopoulos, N., Mona, L., Virtanen, T., Uppstu, A., Sofiev, M., Bugliaro, L., Vázquez-Navarro, M., Hedelt, P., Parks, M. M., Barsotti, S., Coltelli, M., Moreland, W., Arnold-Arias, D., Hirtl, M., Peltonen, T., Lahtinen, J., Sievers, K., Lipok, F., Rüfenacht, R., Haefele, A., Hervo, M., Wagenaar, S., Som de Cerff, W., de Laat, J., Apituley, A., Stammes, P., Laffineur, Q., Delcloo, A., Lennart, R., Rokitansky, C.-H., Vargas, A., Kerschbaum, M., Resch, C., Zopp, R., Plu, M., Peuch, V.-H., Van Roozendael, M., and Wotawa, G.: EUNADICS early warning system dedicated to support aviation in case of crisis from natural airborne hazard and radionuclide cloud, Nat. Hazards Earth Syst. Sci., accepted (2021).

Theys, N., De Smedt, I., Yu, H., Danckaert, T., van Gent, J., Hörmann, C., Wagner, T., Hedelt, P., Bauer, H., Romahn, F., Pedergnana, M., Loyola, D., and Van Roozendael, M.: Sulfur dioxide retrievals from TROPOMI onboard Sentinel-5 Precursor: algorithm theoretical basis, Atmos. Meas. Tech., 10, 119–153 (2017).

Theys, N., Hedelt, P., De Smedt, I. et al. Global monitoring of volcanic SO2 degassing with unprecedented resolution from TROPOMI onboard Sentinel-5 Precursor. Sci Rep 9, 2643 (2019).

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., and Van Roozendael, M.: A Sulfur Dioxide Covariance-Based Retrieval Algorithm (COBRA): application to TROPOMI reveals new emission sources, Atmos. Chem. Phys. Discuss., accepted (2021).

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