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Re‐evaluation of SO 2 release of the 15 June 1991 Pinatubo eruption using ultraviolet and infrared satellite sensors

2004; Wiley; Volume: 5; Issue: 4 Linguagem: Inglês

10.1029/2003gc000654

1525-2027

Song Guo, G. J. Bluth, William I. Rose, I. M. Watson, Fred Prata,

Atmospheric and Environmental Gas Dynamics

In this study, ultraviolet TOMS (Total Ozone Mapping Spectrometer) satellite data for SO 2 are re‐evaluated for the first 15 days following the 15 June 1991 Pinatubo eruption to reflect new data retrieval and reduction methods. Infrared satellite SO 2 data from the TOVS/HIRS/2 (TIROS (Television Infrared Observation Satellite) Optical Vertical Sounder/High Resolution Infrared Radiation Sounder/2) sensor, whose data sets have a higher temporal resolution, are also analyzed for the first time for Pinatubo. Extrapolation of SO 2 masses calculated from TOMS and TOVS satellite measurements 19–118 hours after the eruption suggest initial SO 2 releases of 15 ± 3 Mt for TOMS and 19 ± 4 Mt for TOVS, including SO 2 sequestered by ice in the early Pinatubo cloud. TOVS estimates are higher in part because of the effects of early formed sulfate. The TOMS SO 2 method is not sensitive to sulfate, but can be corrected for the existence of this additional emitted sulfur. The mass of early formed sulfate in the Pinatubo cloud can be estimated with infrared remote sensing at about 4 Mt, equivalent to 3 Mt SO 2 . Thus the total S release by Pinatubo, calculated as SO 2 , is 18 ± 4 Mt based on TOMS and 19 ± 4 Mt based on TOVS. The SO 2 removal from the volcanic cloud during 19–374 hours of atmospheric residence describes overall e‐folding times of 25 ± 5 days for TOMS and 23 ± 5 days for TOVS. These removal rates are faster in the first 118 hours after eruption when ice and ash catalyze the reaction, and then slow after heavy ash and ice fallout. SO 2 mass increases in the volcanic cloud are observed by both TOMS and TOVS during the first 70 hours after eruption, most probably caused by the gas‐phase SO 2 release from sublimating stratospheric ice‐ash‐gas mixtures. This result suggests that ice‐sequestered SO 2 exists in all tropical volcanic clouds, and at least partially explains SO 2 mass increases observed in other volcanic clouds in the first day or two after eruption.