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

Bromine monoxide (BrO) is a halogen radical capable of influencing atmospheric chemical processes, in particular the abundance of ozone, e. g. in the polar boundary layer and above salt lakes, in 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.

To monitor volcanic activities on global scale, satellite measurements provide invaluable information. For these purposes, the TROPOspheric Monitoring Instrument (TROPOMI) onboard ESA’s S5-P satellite is particularly interesting: its high spatial resolution of up to 3.5x5.5km² and daily global coverage offer great potential to detect BrO and its corresponding ratio with sulphur dioxide (BrO/SO₂) even during minor eruptions and for continuous passive degassing volcanoes.

Here, we present a global overview of BrO/SO₂ molar ratios in volcanic plumes derived from a systematic long-term investigation covering four years (Januar 2018 to December 2021) of TROPOMI data.

We retrieved column densities of BrO and SO₂ using Differential Optical Absorption Spectroscopy (DOAS) and calculated mean BrO/SO₂ molar ratios for various volcanoes. The calculated BrO/SO₂ molar ratios differ strongly between different volcanoes, but also between measurements at one volcano at different points in time, ranging from several 10^-5 up to several 10^-4. In our four-year study of S5P/TROPOMI data we successfully recorded elevated BrO column densities at 506 volcanic events. We were able to derive significant BrO/SO₂ ratios at 26 different volcanoes on 378 occasions, thus adding an important volcanic parameter to these volcanoes.

In addition, this large data set of events allows to deduce time-series of several very active volcanoes, such as Mount Etna, Italy and Ambrym, Vanuatu.