THE ATMOSPHERIC SO(2) BUDGET FOR PINATUBO DERIVED FROM NOAA-11 SBUV 2SPECTRAL DATA/

Spectral scan data from the NOAA-11 SBUV/2 instrument were used to der ive SO2 for three days following the eruption of Mt. Pinatubo - June 1 9, July 1, and July 17, 1991. Band structure between 300 and 310 nm ob served in the backscattered albedo uniquely identifies the presence of SO2. Band ratios are used to infer SO2 amounts to better accuracy (ap proximately 10% to 20%) and sensitivity (about 0.5 milli-atm-cm of SO2 ) than the TOMS retrieval, but with relatively poor spatial coverage b ecause the measurement is nadir only. Only 7 scans showed detectable S O2 on June 19 when the cloud was still very localized. On July 1 there were 29 scans between 35-degrees-N and 12-degrees-S with SO2, with th e highest concentration detected over the Atlantic, and on July 17 SO2 was detected in 30 scans around the world, but in decreased concentra tion. Estimates of the total SO2 budget made after the cloud had sprea d sufficiently for the sparse SBUV/2 sampling to be adequate indicated that there were 8.4 million metric tons (MMT) of SO2 in the stratosph ere on July 1, 1991, and 4.1 MMT remaining on July 17. This correspond s to an e-folding time of about 24 days for the conversion of SO2 to a erosol, and is consistent with an initial injection into the stratosph ere of 12-15 MMT of SO2.