The atmospheric SO 2 budget for Pinatubo derived from Noaa‐11 SBUV/2 spectral data

Spectral scan data from the NOAA‐11 SBUV/2 instrument were used to derive SO 2 for three days following the eruption of Mt. Pinatubo ‐ June 19, July 1, and July 17, 1991. Band structure between 300 and 310 nm observed in the backscattered albedo uniquely identifies the presence of SO 2 . Band ratios are used to infer SO 2 amounts to better accuracy (∼10% to 20%) and sensitivity (about 0.5 milli‐atm‐cm of SO 2 ) than the TOMS retrieval, but with relatively poor spatial coverage because the measurement is nadir only. Only 7 scans showed detectable SO 2 on June 19 when the cloud was still very localized. On July 1 there were 29 scans between 35°N and 12°S with SO 2 , with the highest concentration detected over the Atlantic, and on July 17 SO 2 was detected in 30 scans around the world, but in decreased concentration. Estimates of the total SO 2 budget made after the cloud had spread sufficiently for the sparse SBUV/2 sampling to be adequate indicated that there were 8.4 million metric tons (MMT) of SO 2 in the stratosphere on July 1, 1991, and 4.1 MMT remaining on July 17. This corresponds to an e‐folding time of about 24 days for the conversion of SO 2 to aerosol, and is consistent with an initial injection into the stratosphere of 12–15 MMT of SO 2 .