Abstract
Abstract. During recent years, volcanic emissions turned out to be a natural source of bromine compounds in the atmosphere. While the initial formation process of bromine monoxide (BrO) has been successfully studied in local ground-based measurements at quiescent degassing volcanoes worldwide, literature on the chemical evolution of BrO on large spatial and temporal scales is sparse. The first space-based observation of a volcanic BrO plume following the Kasatochi eruption in 2008 demonstrated the capability of satellite instruments to monitor such events on a global scale. In this study, we systematically examined GOME-2 observations from January 2007 until June 2011 for significantly enhanced BrO slant column densities (SCDs) in the vicinity of volcanic plumes. In total, 772 plumes from at least 37 volcanoes have been found by using sulphur dioxide (SO2) as a tracer for a volcanic plume. All captured SO2 plumes were subsequently analysed for a simultaneous enhancement of BrO and the data were checked for a possible spatial correlation between the two species. Additionally, the mean BrO/SO2 ratios for all volcanic plumes have been calculated by the application of a bivariate linear fit. A total number of 64 volcanic plumes from at least 11 different volcanoes showed clear evidence for BrO of volcanic origin, revealing large differences in the BrO/SO2 ratios (ranging from some 10−5 to several 10−4) and the spatial distribution of both species. A close correlation between SO2 and BrO occurred only for some of the observed eruptions or just in certain parts of the examined plumes. For other cases, only a rough spatial relationship was found. We discuss possible explanations for the occurrence of the different spatial SO2 and BrO distributions in aged volcanic plumes.
Highlights
Ground-based measurements at quiescent degassing volcanoes worldwide, literature on the chemical evolution of bromine monoxide (BrO) on large spatial and temporal scales is sparse
We cross-checked our data with online reports on the Global Volcanism Programme (GVP) website of the Smithsonian Institution and with daily SO2 maps from the Ozone Monitoring Instrument (OMI, http://so2.gsfc.nasa.gov/), the latter providing a more detailed spatial resolution of up to 13 × 25 km2 and daily global coverage
Volcanic plumes were systematically extracted from the GOME-2 dataset during the time period between January 2007 and June 2011 (1642 days) by using SO2 as a tracer for the plumes’ extent
Summary
The GOME-2 (Global Ozone Monitoring Experiment-2) is the first of three identical instruments that are part of the MetOp satellite series operated by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). GOME-2 is a 4 channel UV/Vis grating spectrometer that observes the Earth’s atmosphere in nadir viewing geometry. By scanning the earth surface with a swath-width of 1920 km (including viewing angles up to 50◦ off-nadir), global coverage is achieved within 1.5 days (EUMETSAT, 2005; Munro et al, 2006). GOME-2 measures both the radiance component of sunlight reflected by the Earth’s atmosphere and the direct sunlight, covering the wavelength region of 240– 790 nm at moderate spectral resolution of 0.2–0.4 nm. With a pixel size of 40 × 80 km, GOME-2 observes 4 times smaller ground pixels than its predecessor GOME on ERS-2
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