A comparison of satellite- and ground-based measurements of SO2 emissions from Tungurahua volcano, Ecuador

Abstract

Satellite-measured SO 2 mass loadings and ground-based measurements of SO 2 emission rate are not directly comparable, with ∼ 40% differences between mean emissions reported by each technique from Tungurahua volcano, Ecuador, during late 2007. Numerical simulations of post-emission processing and dispersal of Tungurahua's SO 2 emissions enable more effective comparison of ground- and satellite-based SO 2 datasets, reducing the difference between them, and constraining the impact of plume processing on satellite SO 2 observations. Ground-based measurements of SO 2 emission rate are used as the model input, and simulated SO 2 mass loadings are compared to those measured by the Ozone Monitoring Instrument (OMI). The changing extent of SO 2 processing has a significant impact on daily variation in SO 2 mass loading for a fixed volcanic emission rate. However, variations in emission rate at Tungurahua are large, suggesting that overall volcanic source strength and not subsequent processing is more likely to be the dominant control on atmospheric mass loading. SO 2 emission rate estimates are derived directly from the OMI observations using modelled SO 2 lifetime. Good agreement is achieved between both observed and simulated mass loadings (∼ 21%), and satellite-derived and ground-measured SO 2 emission rates (∼ 18%); a factor of two improvement over the differences found by simple direct comparison. Whilst the balance ofemission source strength and post-emission processing will differ between volcanoes and regions, under good observation conditions and where SO 2 lifetime is ∼ 24 hours, satellite-based sensors like OMI may provide daily observations of SO 2 mass loading which are a good proxy for volcanic source strength.