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

A W Rollins; T D Thornberry; L A Watts; P Yu; K H Rosenlof; M Mills; E Baumann; F R Giorgetta; T V Bui; M Höpfner; K A Walker; C Boone; P F Bernath; P R Colarco; P A Newman; D W Fahey; R S Gao

doi:10.1002/2017GL072754

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

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

Authors

A W Rollins^{1

2}, T D Thornberry^{1

2}, L A Watts^{1

2}, P Yu^{1

2}, K H Rosenlof², M Mills³, E Baumann⁴, F R Giorgetta⁴, T V Bui⁵, M Höpfner⁶, K A Walker^{7

8}, C Boone⁸, P F Bernath^{8

9}, P R Colarco¹⁰, P A Newman¹⁰, D W Fahey^{1

2}, R S Gao²

Affiliations

¹ Cooperative Institute for Research in Environmental Sciences, Boulder, CO, USA.
² NOAA Earth System Research Laboratory, Chemical Sciences Division, Boulder, CO, USA.
³ National Center for Atmospheric Research, Boulder, CO, USA.
⁴ National Institute of Standards and Technology, Boulder, CO, USA.
⁵ NASA Ames Research Center, Moffett Field, CA, USA.
⁶ Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany.
⁷ Department of Physics, University of Toronto, Toronto, ON, Canada.
⁸ Department of Chemistry, University of Waterloo, Waterloo, ON, Canada.
⁹ Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA, USA.
¹⁰ NASA Goddard Space Flight Center, Greenbelt, MD, USA Corresponding author: Andrew Rollins.

Abstract

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.

Abstract

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