H2SO4 photolysis: A souce of sulfur dioxide in the upper stratosphere

Numerous absoption lines of stratospheric sulfer dioxide (SO2) were identified in solar occulation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Science (ATLAS)-1 shuttle mission (March 24-April 2, 1992). based on their analysis, a volume mixing ratio profile of SO2 increasing from (13 +/- 4) p.p.t.v. (parts per 10(exp -12) by volume) at 16 mbar (approximately 28 km) to 455 +/- 90 p.p.t.v. at 0.63 mbar (approximately 52 km) was measured with no significant profile differences between 20 deg N and 60 deg S latitude. The increase in the SO2 mixing ratios with altitude indicates the presence of a source of SO2 in the upper stratosphere. Profiles retrieved from ATMOS spectra recorded during shuttle flights in April-May 1985 and April 1993 show similar vertical distributions but lower concentrations. Two-dimensional model calculations with SO2 assumed as the end product of H2SO4 photolysis produce SO2 profiles consistent with the ATMOS measuremnts to within about a factor 2.