Volcanic SO2 – The disparity between satellite observations and the AeroCOM database

Abstract:

Volcanoes are the largest natural source of SO₂ in the world and volcanic SO₂ is an important aerosol precursor in many atmospheric composition and climate simulations. The current AeroCOM database for volcanic SO₂ has been compiled from both publications and assumptions about volcanic degassing behavior and includes over 36,000 named and unnamed volcanic sources. However, satellite observations compiled from the Ozone Monitoring Instrument (OMI), aboard NASA’s Aura satellite, the Ozone Mapping Profiler Suite (OMPS), aboard NOAA/NASA’s Suomi NPP satellite, and other satellite based SO₂ observing instruments do not support many of the estimates made for volcanic SO₂ in the current database. For example, the current database significantly overestimates SO₂ from Barren Island in December 2008 and significantly underestimates the SO₂ erupted from Ambrym during the same month. Additionally, all of the volcanoes in the database are assumed to be degassing continually to some extent, an assumption that is not supported by satellite observations.

We present three CTM GEOS-Chem simulations, run from 2007 to 2008, in order to highlight these issues. The first simulation includes the existing AeroCOM SO₂ database and a few select eruptions from this simulation will be compared in detail to satellite observations made over the same period of time. The second simulation will be run with all of the volcanic SO₂ removed in order to examine the sensitivity of the global SO₂ budget to volcanic contributions. Finally, the third simulation will be run with updated values of volcanic SO₂ at specific sources that are based on satellite observations during the corresponding time period. The existing AeroCOM volcanic SO₂ database is robust but, in many cases, is also based on outdated degassing estimates and assumptions that do not agree with our increasing body of satellite observations. Improving the database has the potential to improve model chemistry for a wide community of users.