Tropospheric sulfate from the degassing of SO2 from volcanos can represent a major fraction of sulfate in impacted areas and can contribute disproportionately to tropospheric sulfate burdens globally because of elevated release height, resultant greater conversion of SO2 to sulfate, and long lifetime in the atmosphere.
The accompanying animations show the sulfate plumes (vertical integral of concentration) resulting from volcanic emissions during June and July, 1997, as represented in an Eulerian model driven by observation-derived meteorological data. During this period there were substantial emissions from Mount Etna, Italy, and Popocatepetl, central Mexico. As the volcanic sources are relatively sparse, it is possible to follow individual plumes, as shown in the figure, which represents the model output for June 23, 1997, at 0600UT.
The animation is in QuickTime (R) (16 Mbyte) format. If you have the appropriate plug-in it can be viewed from your browser. Otherwise it can be downloaded and viewed with suitable software. Recommended playback speed is 4 or 8 frames a second. Note: 4 frames represent one day of model time. To be fully appreciated the movie as a whole or a portion of particular interest should be played as a repeating loop.
Volcanic Sulfate 
Popocatepetl is a continually degassing volcano located in Central Mexico (98.62 deg W, 19.02 deg N). On June 16, 1997 Popocatepetl had a major degassing event, emitting ~2 x 107 kg sulfur. Initially sulfate burden built up and remained relatively stationary over the source region (June 17-23); during this period the synoptic scale flow was dominated by a col between a strong ridge to the west of the volcano and a trough to the east; the low level flow was weak and nearly stagnant over the source region. On June 23, a moderately strong trough with its axis along the California coast slipped southward along the Baja Peninsula creating a band of southwesterly winds over the source region. These southwesterly winds extended well into the continental United States, providing a means for the large sulfate burden to advect to the northeast.
Vertical profiles of the modeled sulfate mixing ratio on June 27 showed a maximum MR of 0.5 ppb at the surface, with anthropogenic emissions from North America contributing almost 100%. On June 28 the maximum mixing ratio was ~1.7 ppb at a height of ~4 km, with the volcano emissions contributing over 80%.
Comparisons between modeled column burdens and measured aerosol optical thickness establish confidence in the model results. The model allows attribution of the increase in aerosol optical thickness and surface concentrations to volcanic sources and demonstrates the long range transport of these aerosols.
References:
Effects of Sulfur Emissions from Popocatepetl Volcano on the Central U.S. in June 1997. Benkovitz C. M., Miller M. A., Schwartz S. E., and Easter R. E.. American Geophysical Union Fall Meeting, San Francisco, December 15-19, 2000.
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This page was last updated 2006-01-10.