A global perspective on Bromine monoxide composition in volcanic plumes derived from three years of S5-P/TROPOMI data

Bromine monoxide (BrO) is a halogen radical capable of influencing atmospheric chemical processes, in particular the abundance of ozone, e. g. in the troposphere of polar regions, the stratosphere as well as in volcanic plumes. Furthermore, the molar bromine to sulphur ratio in volcanic gas emissions is a proxy for the magmatic composition of a volcano and potentially an eruption forecast parameter.

The high spatial resolution of the S5-P/TROPOMI instrument (up to 3.5x5.5km²) and its daily global coverage offer the potential to detect BrO even during minor eruptions and also to determine BrO/SO₂ ratios during continuous passive degassing.

Here, we present a global overview of BrO/SO₂ molar ratios in volcanic plumes derived from a systematic long-term investigation of three years of TROPOMI data.

We retrieved column densities of BrO and SO₂ using Differential Optical Absorption Spectroscopy (DOAS) and calculated mean BrOSO₂ molar ratios for each volcano. As expected, the calculated BrO/SO₂ molar ratios differ strongly between different volcanoes ranging from several 10^-5 up to several 10^-4. In our study of three years of S5P/TROPOMI data we successfully recorded elevated BrO column densities for more than 100 volcanic events and were able to derive meaningful (coefficient of determination, R² exceeding 0.5) BrO/SO₂ ratios for multiple volcanoes.