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Geophys Res Lett. 2017 May 16;44(9):4280-4286. doi: 10.1002/2017GL072754. Epub 2017 May 3.

The Role of Sulfur Dioxide in Stratospheric Aerosol Formation Evaluated Using In-Situ Measurements in the Tropical Lower Stratosphere.

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Cooperative Institute for Research in Environmental Sciences, Boulder, CO, USA.
NOAA Earth System Research Laboratory, Chemical Sciences Division, Boulder, CO, USA.
National Center for Atmospheric Research, Boulder, CO, USA.
National Institute of Standards and Technology, Boulder, CO, USA.
NASA Ames Research Center, Moffett Field, CA, USA.
Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Department of Physics, University of Toronto, Toronto, ON, Canada.
Department of Chemistry, University of Waterloo, Waterloo, ON, Canada.
Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA, USA.
NASA Goddard Space Flight Center, Greenbelt, MD, USA Corresponding author: Andrew Rollins.


Stratospheric aerosols (SAs) are a variable component of the Earth's albedo that may be intentionally enhanced in the future to offset greenhouse gases (geoengineering). The role of tropospheric-sourced sulfur dioxide (SO2) in maintaining background SAs has been debated for decades without in-situ measurements of SO2 at the tropical tropopause to inform this issue. Here we clarify the role of SO2 in maintaining SAs by using new in-situ SO2 measurements to evaluate climate models and satellite retrievals. We then use the observed tropical tropopause SO2 mixing ratios to estimate the global flux of SO2 across the tropical tropopause. These analyses show that the tropopause background SO2 is about 5 times smaller than reported by the average satellite observations that have been used recently to test atmospheric models. This shifts the view of SO2 as a dominant source of SAs to a near-negligible one, possibly revealing a significant gap in the SA budget.

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