Persisting volcanic ash particles impact stratospheric SO2 lifetime and aerosol optical properties

Yunqian Zhu; Owen B Toon; Eric J Jensen; Charles G Bardeen; Michael J Mills; Margaret A Tolbert; Pengfei Yu; Sarah Woods

doi:10.1038/s41467-020-18352-5

Persisting volcanic ash particles impact stratospheric SO₂ lifetime and aerosol optical properties

Nat Commun. 2020 Sep 10;11(1):4526. doi: 10.1038/s41467-020-18352-5.

Authors

Yunqian Zhu¹, Owen B Toon^{2

3}, Eric J Jensen⁴, Charles G Bardeen⁴, Michael J Mills⁴, Margaret A Tolbert⁵, Pengfei Yu^{6

7}, Sarah Woods⁸

Affiliations

¹ Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, 80303, USA. yunqian.zhu@colorado.edu.
² Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, 80303, USA.
³ Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, 80302, USA.
⁴ Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO, 80301, USA.
⁵ Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, 80309, USA.
⁶ Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, 80305, USA.
⁷ Institute for Environmental and Climate Research, Jinan University, Guangzhou, China.
⁸ Stratton Park Engineering Company, Inc, Bo ulder, CO, 80301, USA.

Abstract

Volcanic ash is often neglected in climate simulations because ash particles are assumed to have a short atmospheric lifetime, and to not participate in sulfur chemistry. After the Mt. Kelut eruption in 2014, stratospheric ash-rich aerosols were observed for months. Here we show that the persistence of super-micron ash is consistent with a density near 0.5 g cm^-3, close to pumice. Ash-rich particles dominate the volcanic cloud optical properties for the first 60 days. We also find that the initial SO₂ lifetime is determined by SO₂ uptake on ash, rather than by reaction with OH as commonly assumed. About 43% more volcanic sulfur is removed from the stratosphere in 2 months with the SO₂ heterogeneous chemistry on ash particles than without. This research suggests the need for re-evaluation of factors controlling SO₂ lifetime in climate model simulations, and of the impact of volcanic ash on stratospheric chemistry and radiation.