The Contribution of Volcanic gas and Particle Emissions to the Troposphere

Volcanoes release considerable fluxes of gases and particles to the atmosphere, both during eruptions and during long-term non-eruptive degassing. While the volcanic fluxes of many species are very poorly known (often only to 1 or 2 orders of magnitude), the volcanic contribution to the tropospheric burden of certain gases (including SO2, HCl, HF, BrO); volatile trace metals (including Cd, Hg, Zn) and aerosol (including sulphate) is certainly significant. In terms of sulphur dioxide, most of the long-term time-averaged volcanic emission is from non-erupting volcanoes (6-9 Tg/yr), or during relatively minor eruptions (6-8 Tg/yr), rather than from large explosive eruptions (1-2 Tg/yr). Emissions from `passively degassing' volcanoes are significant since they are mostly to the free troposphere (due to the vent elevation, or the plume rise height) where species lifetimes are extended, and the impact of volcanic sources is enhanced. Volcanic emissions are not limited to species released directly from magma, but also include those produced by chemical reaction in the extreme environments associated with the volcano. Newly discovered volcano-related gases include NOx and HNO3, which form by thermal decomposition of atmospheric nitrogen at the magma-air interface, and halocarbons produced by reactions between volcanic fluids and surrounding materials. We report early progress in the development of a new temporally- and spatially resolved global volcanic emissions budget that is designed to represent a broader spectrum of volcanogenic species than is currently available, and which will be used a focus for detailed analysis of the sensitivity of the atmosphere to sustained volcanic emissions.