In situ measurements of tropospheric volcanic plumes in Ecuador and Colombia...

Carn, S. A., K. Froyd, B. E. Anderson, P. Wennberg, J. D. Crounse, K. Spencer, J. Dibb, N. Krotkov, E. Browell, J. W. Hair, G. S. Diskin, G. Sachse, and S. A. Vay (2011), In situ measurements of tropospheric volcanic plumes in Ecuador and Colombia during TC4, J. Geophys. Res., 116, D00J24, doi:10.1029/2010JD014718.

A NASA DC‐8 research aircraft penetrated tropospheric gas and aerosol plumes sourced from active volcanoes in Ecuador and Colombia during the Tropical Composition, Cloud and Climate Coupling (TC4) mission in July–August 2007. The likely source volcanoes were Tungurahua (Ecuador) and Nevado del Huila (Colombia). The TC4 data provide rare insight into the chemistry of volcanic plumes in the tropical troposphere and permit a comparison of SO2 column amounts measured by the Ozone Monitoring Instrument (OMI) on the Aura satellite with in situ SO2 measurements. Elevated concentrations of SO2, sulfate aerosol, and particles were measured by DC‐8 instrumentation in volcanic outflow at altitudes of 3–6 km. Estimated plume ages range from ∼2 h at Huila to ∼22–48 h downwind of Ecuador. The plumes contained sulfate‐rich accumulation mode particles that were variably neutralized and often highly acidic. A significant fraction of supermicron volcanic ash was evident in one plume. In‐plume O3 concentrations were ∼70%–80% of ambient levels downwind of Ecuador, but data are insufficient to ascribe this to O3 depletion via reactive halogen chemistry. The TC4 data record rapid cloud processing of the Huila volcanic plume involving aqueous‐phase oxidation of SO2 by H2O2, but overall the data suggest average in‐plume SO2 to sulfate conversion rates of ∼1%–2% h−1. SO2 column amounts measured in the Tungurahua plume (∼0.1–0.2 Dobson units) are commensurate with average SO2 columns retrieved from OMI measurements in the volcanic outflow region in July 2007. The TC4 data set provides further evidence of the impact of volcanic emissions on tropospheric acidity and oxidizing capacity.

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