Enhanced sulfur in the upper troposphere and lower stratosphere in spring 2020
Laura Tomsche (Johannes Gutenberg-University Mainz, Deutsches Zentrum für Luft- und Raumfahrt (DLR))
Andreas Marsing (Johannes Gutenberg-University Mainz, Deutsches Zentrum für Luft- und Raumfahrt (DLR))
Tina Jurkat-Witschas (Deutsches Zentrum für Luft- und Raumfahrt (DLR))
J.R. Lucke (Deutsches Zentrum für Luft- und Raumfahrt (DLR), TU Delft - Aerospace Engineering)
Stefan Kaufmann (Deutsches Zentrum für Luft- und Raumfahrt (DLR))
Katharina Kaiser (Max Planck Institute of Chemistry)
Johannes Schneider (Max Planck Institute of Chemistry)
Monika Scheibe (Deutsches Zentrum für Luft- und Raumfahrt (DLR))
Hans Schlager (Deutsches Zentrum für Luft- und Raumfahrt (DLR))
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Abstract
Sulfur compounds in the upper troposphere and lower stratosphere (UTLS) impact the atmosphere radiation budget, either directly as particles or indirectly as precursor gas for new particle formation. In situ measurements in the UTLS are rare but are important to better understand the impact of the sulfur budget on climate. The BLUESKY mission in May and June 2020 explored an unprecedented situation. (1) The UTLS experienced extraordinary dry conditions in spring 2020 over Europe, in comparison to previous years, and (2) the first lockdown of the COVID-19 pandemic caused major emission reductions from industry, ground, and airborne transportation. With the two research aircraft HALO and Falcon, 20 flights were conducted over central Europe and the North Atlantic to investigate the atmospheric composition with respect to trace gases, aerosol, and clouds. Here, we focus on measurements of sulfur dioxide (SO2) and particulate sulfate (SO42-) in the altitude range of 8 to 14.5gkm which show unexpectedly enhanced mixing ratios of SO2 in the upper troposphere and of SO42- in the lowermost stratosphere. In the UT, we find SO2 mixing ratios of (0.07±0.01)gppb, caused by the remaining air traffic, and reduced SO2 sinks due to low OH and low cloud fractions and to a minor extent by uplift from boundary layer sources. Particulate sulfate showed elevated mixing ratios of up to 0.33gppb in the LS. We suggest that the eruption of the volcano Raikoke in June 2019, which emitted about 1gTggSO2 into the stratosphere in northern midlatitudes, caused these enhancements, in addition to Siberian and Canadian wildfires and other minor volcanic eruptions. Our measurements can help to test models and lead to new insights in the distribution of sulfur compounds in the UTLS, their sources, and sinks. Moreover, these results can contribute to improving simulations of the radiation budget in the UTLS with respect to sulfur effects.
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