Sulphur dioxide diffusion tube monitoring: Soufriere Hills Volcano, Montserrat, 1995 to 2011

Sulphur dioxide (SO2) diffusion tube monitoring has been undertaken on Montserrat since 1995, providing a unique and insightful long-term dataset of ground-level SO2 concentrations during the eruption of the Soufriere Hills Volcano (SHV). The monitor- ing of ground-level SO2 is important to assess the potential of human exposure to high levels of SO2 that may impact on health. Air-qualityobjectives for SO2are presentin some countriesto prevent potential health impacts.Here we summarise diffusiontube moni- toring in Montserrat and analyse concentrations with respect to the potential for exposure to levels above recommended levels. We explore relationships that may exist with SO2 flux measurements and volcanic events. Concentrations have been higher during pauses in lava extrusion. Diffusion tube concentrations are highest within 5 km of the volcano and at locations downwind of the plume. Areas where concentrations have exceeded relevant limits have been uninhabited since 1996. The potential for human exposure above recommended limits is, therefore, currently considered low, as the population would not have been exposed to high concentrations for extended periods of time. Full-time occupation and/or long-term exposure in the areas where concentrations exceed the relevant limits would not be advised.