Removal Processes of the Stratospheric SO2 Volcanic Plume From the 2015 Calbuco Eruption

Abstract

We analyze the volcanic plume from the April 2015 Calbuco eruption over a 35-day period using simulations from Meso-NH, a non-hydrostatic mesoscale atmospheric model. A dedicated parameterization of the deep injection of the plume into the stratosphere ensures a realistic representation when compared to Infrared Atmospheric Sounding Interferometer satellite observations. During the first 12 hr of the eruption, on 22 April 2015, SO₂ mixing ratio reached 29 ppmv between 15 and 18 km for the first eruption pulse, and 38 ppmv between 12 and 16 km for the second. Most SO₂ was injected directly into the stratosphere, with a stratospheric load reaching 308 ktS (kilotons of atomic sulfur, i.e. 616 kilotons of SO₂) after the eruption. After 1 month, both stratospheric and tropospheric SO₂ loads returned to near-background levels. During analysis, the chemical conversion of SO₂ into H₂SO₄ removed a part of SO₂ from the stratosphere. During the long-range advection, the co-location between the subtropical jet stream and the Calbuco plume led to three significant stratospheric intrusions on 24, 26 and 28 April 2015. These events transferred stratospheric SO₂ into the troposphere, SO₂ mixing ratios in the upper troposphere reaching 15 ppmv, 26 and 15 ppbv, respectively. SO₂ is gradually oxidized into H₂SO₄, with up to 5 ktS of gaseous H₂SO₄ in the stratosphere on 30 April, but dynamical processes dominate the SO₂ atmospheric budget over chemical transformations. This study demonstrates that stratospheric intrusions can play a critical role in the removal of volcanic material from the stratosphere following a major eruption.