A modelling approach for quantifying volcanic sulphur dioxide concentrations at flight altitudes and the potential hazard to aircraft occupants

Volcanic eruptions can emit large quantities of sulphur dioxide (SO 2 ) into the atmosphere, which can be harmful to people and the environment. Aircraft encounters with a volcanic SO 2 cloud could represent a health hazard to crew and passengers onboard. In this study we have assessed concentration levels of volcanic SO 2 in the atmosphere following eight historic eruptions and use four-dimensional dispersion model simulation data to calculate when and where the World Health Organisation (WHO) health protection guideline for SO 2 of 500 μgm -3 over 10 minutes is exceeded. The time and area of exceedance varies and depends on the eruption characteristics: the amount, duration and height of the SO 2 release. The WHO-based guideline value is exceeded for all historic eruptions considered. In several cases, the area delineated by the WHO-based guideline, here called the SO 2 hazard area, can be considerably larger than the volcanic ash hazard area for the same eruption. SO 2 hazard areas also often extend over a longer period of time compared to the equivalent ash advisories. For example, following the 2019 eruption of Raikoke, the SO 2 hazard area reached up to 1.7 million km 2 and the WHO-based guideline value was exceeded for about two weeks, while volcanic ash was considered hazardous to aviation for about five days. These results will help the aviation industry to better understand the potential risks to their passengers and crew from volcanic SO 2 , and aid in defining concentration thresholds for any potential volcanic SO 2 forecasts for aviation.