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 postemission processing and dispersal of Tungurahua's SO 2 emissions enable more effective comparison of ground-and satellite-based SO 2 data sets, 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 modeled 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%), with a factor of 2 improvement over the differences found by simple direct comparison. While the balance of emission source strength and postemission 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.

Assessment of the Combined Sensitivity of Nadir TIR Satellite Observations to Volcanic SO2 and Sulphate Aerosols after a Moderate Stratospheric Eruption

“…The oxidation phase, and then the time evolution of volcanic SO 2 burdens, is controlled by Equation (1) (e.g., [13,33]), where M SO 2 (t) is the SO 2 mass at a time t, M SO 2 (t 0 ) is the total SO 2 mass loading injected by the volcano (the day of eruption, t = 0) and a is the e-folding time for this process. In our study, we fix SO 2 e-folding time to 3.10 −7 s −1 (about 38 days lifetime), as observed by Oppenheime et al (e.g., [13]), and suggested as a typical value for stratospheric sulphur cycles:…”

Synergistic use of Lagrangian dispersion and radiative transfer modelling with satellite and surface remote sensing measurements for the investigation of volcanic plumes: the Mount Etna eruption of 25–27 October 2013

“…It can be roughly estimated from the generic residence time equation (see e.g. McCormick et al, 2014):…”

“…The downwind impact of volcanic activity can be monitored by groundbased stations, depending on the dynamics of the plume. Efforts for the synergistic use of satellite observations with ground-based measurements and/or modelling have been recently proposed (Webley et al, 2012;McCormick et al, 2014).…”

Using SO 2 camera imagery and seismicity to examine degassing and gas accumulation at Kīlauea Volcano, May 2010

“…Applying the same factor to the May 2010 daily averages gives a higher range from 9.84 kg/s to 23.26 kg/s. Beirle et al (2013) also determined an average monthly emission rate for Kīlauea using GOME-2 satellite data, reporting an even higher value at~60 kg/s (~5000 t/d); such a discrepancy is not unexpected given the documented difficulty of direct satellite-to-ground-based SO 2 measurement comparisons, especially for tropospheric, persistent plumes (e.g., McCormick et al, 2014).…”