Evaluation of Redoubt Volcano's sulfur dioxide emissions by the Ozone Monitoring Instrument

摘要

The 2009 eruption of Redoubt Volcano, Alaska, provided a rare opportunity to compare satellite measurements of sulfur dioxide (SO_2) by the Ozone Monitoring Instrument (OMI) with airborne SO_2 measurements by the Alaska Volcano Observatory (AVO). Herein we: (1) compare OMI and airborne SO_2 column density values for Redoubt's tropospheric plume, (2) calculate daily SO_2 masses from Mount Redoubt for the first three months of the eruption, (3) develop simple methods to convert daily measured SO_2 masses into emission rates to allow satellite data to be directly integrated with the airborne SO_2 emissions dataset, (4) calculate cumulative SO_2 emissions from the eruption, and (5) evaluate OMI as a monitoring tool for high-latitude degassing volcanoes. A linear correlation (R~2～0.75) is observed between OMI and airborne SO_2 column densities. OMI daily SO_2 masses for the sample period ranged from ～60.1 kt on 24 March to below detection limit, with an average daily SO_2 mass of～6.7 kt. The highest SO_2 emissions were observed during the initial part of the explosive phase and the emissions exhibited an overall decreasing trend with time. OMI SO_2 emission rates were derived using three methods and compared to airborne measurements. This comparison yields a linear correlation (R~2～0.82) with OMI-derived emission rates consistently lower than airborne measurements. The comparison results suggest that OMI's detection limit for high latitude, springtime conditions varies from ～2000 to 4000 t/d. Cumulative SO_2 masses calculated from daily OMI data for the sample period are estimated to range from 542 to 615 kt, with approximately half of this SO_2 produced during the explosive phase of the eruption. These cumulative masses are similar in magnitude to those estimated for the 1989-90 Redoubt eruption. Strong correlations between daily OMI SO_2 mass and both tephra mass and acoustic energy during the explosive phase of the eruption suggest that OMI data may be used to infer relative eruption size and explosivity. Further, when used in conjunction with complementary datasets, OMI daily SO_2 masses may be used to help distinguish explosive from effusive activity and identify changes in lava extrusion rates. The results of this study suggest that OMI is a useful volcano monitoring tool to complement airborne measurements, capture explosive SO_2 emissions, and provide high temporal resolution SO_2 emissions data that can be used with interdisciplinary datasets to illuminate volcanic processes.