My current research focus is the application of remote sensing data to studies of volcanic degassing, volcanic eruption clouds, and anthropogenic pollution. Space-borne sensors such as the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite now allow us to probe the chemistry of the lower troposphere and measure the abundance of sulfur dioxide (SO2), ozone, bromine monoxide (BrO), nitrogen dioxide (NO2) and other important trace gases with unprecedented sensitivity. The cross-platform sensor synergy provided by NASA’s A-Train satellite constellation is advancing our knowledge of volcanic cloud composition and transport. My main focus is SO2, a precursor of sulfate aerosol, which plays an important role in the atmosphere through negative climate forcing and impacts on cloud microphysics. The spatiotemporal variability of natural and anthropogenic SO2 emissions, and hence of global sulfate aerosol abundance, is poorly constrained, impacting the accuracy of climate models.