Volcanic sulfur dioxide measurements from the total ozone mapping spectrometer instruments

Abstract

The total ozone mapping spectrometer (TOMS), first flown on the Nimbus 7 satellite, has delivered an unanticipated set of unique information about volcanic plumes because of its contiguous spatial mapping and use of UV wavelengths. The accuracies of TOMS sulfur dioxide retrievals, volcanic plume masses, and eruption totals under low‐latitude conditions are evaluated using radiative transfer simulations and error analysis. The retrieval algorithm is a simultaneous solution of the absorption optical depth equations including ozone and sulfur dioxide at the four shortest TOMS wavelengths and an empirical correction based on background condition residuals. The retrieval algorithm reproduces model stratospheric sulfur dioxide plume amounts within ±10% over most central scan angles and moderate solar zenith angles if no aerosols or ash are present. The errors grow to 30% under large solar zenith angle conditions. Volcanic ash and sulfate aerosols in the plume in moderate optical depths (0.3) produce an overestimation of the sulfur dioxide by 15–25% depending on particle size and composition. Retrievals of tropospheric volcanic plumes are affected by the reflectivity of the underlying surface or clouds. The precision of individual TOMS SO2 soundings is limited by data quantization to ±6 Dobson units. The accuracy is independent of most instrument calibration errors but depends linearly on relative SO2 absorption cross‐section errors at the TOMS wavelengths. Volcanic plume mass estimates are dependent on correction of background offsets integrated over the plume area. The errors vary with plume mass and area, thus are highly individual. In general, they are least for moderate size, compact plumes. Estimates of the total mass of explosively erupted sulfur dioxide depend on extrapolation of a series of daily plume masses backward to the time of the eruption. Errors of 15–30% are not unusual. Effusive eruption total mass estimates are more uncertain due to difficulties in separating new from old sulfur dioxide in daily observations.

BrO emission from volcanoes: A survey using GOME and SCIAMACHY measurements

“…[3] SO 2 from volcanic eruptions has also been observed from space [e.g., Krueger et al, 1995;Eisinger and Burrows, 1998], but the retrieval of volcanic BrO from satellite measurements has never been reported in literature before. In order to assess how representative the measurements of Bobrowski et al are on a global scale, more measurements of volcanic plumes are needed.…”

Redox control of sulfur degassing in silicic magmas

“…Finally, the ratio mass of fluid/(mass of erupted magma) gives the wt % fluid coexisting at depth in the magma chamber. Since the TOMS-based estimates of sulfur may not record the sulfate adsorbed on ashes directly carried down to the ground following eruption, as shown by Varekamp et al [1984] for the E1 Chich6n eruption and as suggested for most other eruptions (J. Luhr, personal communication, 1998), the fluid wt % listed in Table 1 are probaly minimum values (see also Krueger et al [1995] for TOMS limitations in volcanic SO 2 retrievals). For Mount St. Helens, experimental evidence [Rutherford and Devine, 1988] shows that prior to May 18, 1980 eruption the mole fraction of H20 in the fluid phase was 0.67, assuming that the magma was volatile-saturated.…”

A comparison of thermal infrared and ultraviolet retrievals of SO2 in the cloud produced by the 2003 Al‐Mishraq State sulfur plant fire

“…Etna [Realmuto et al, 1994]. The EP TOMS data was processed using the standard 4-band inversion technique for SO 2 clouds [Krueger et al, 1995]. Errors for this method are +10%/À20% for a low solar zenith angle assuming sulfate aerosols collocated with SO 2 has a moderate optical depth [Krueger et al, 1995].…”