Systematic investigation of bromine monoxide in volcanic plumes from space by using the GOME-2 instrument

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.