资源环境科技发展态势分析平台

Halogens are emitted from volcanoes primarily as hydrogen halides (HCl, HF, HBr, and HI). Upon mixing with the atmosphere, chlorine and bromine species are partially converted to the halogen oxides OClO and BrO. Here we report on the spatial distribution of BrO and OClO in the gas plume emitted from Mount Pagan volcano, Northern Mariana Islands. We found enhanced BrO/SO2 ratios near the plume edges and a lack of OClO in the plume's core. Our results highlight the importance of in-mixing of atmospheric oxidants for halogen oxide formation. They indicate that OClO can only be formed after most bromide dissolved in plume aerosols has been released to the gas phase. We conclude that Mount Pagan's gas emissions originated from a shallow magma body and were transported to the surface along dry degassing pathways and that the volcano's halogen emissions likely had significant impact on the oxidation capacity of the downwind atmosphere.

Plain Language Summary The halogens chlorine, fluorine, bromine, and iodine are commonly degassed from volcanoes and can cause ozone destruction in downwind areas. This occurs through a series of complex chemical reactions taking place within the first few minutes after emission that convert part of the emitted bromine and chlorine into bromine monoxide (BrO) and chlorine dioxide (OClO). These halogen oxides can be measured using remote sensing instruments commonly used to monitor volcanic degassing around the world. In this study, we examine the spatial distribution of BrO and OClO in the plume of Mount Pagan volcano. Our measurements allow insights into the chemical processes responsible for BrO and OClO formation. We find that in-mixing of background air is of fundamental importance for the reaction scheme and that BrO is formed preferentially over OClO. This information will allow volcanologists to better link bromine emissions to associated volcanic activity and help in assessing the impact of volcanic halogen degassing on atmospheric chemistry.