Modelling the atmospheric chemistry of volcanic plumes

Volcanoes are the principal way by which volatiles are transferred from the solid Earth to the atmosphere-hydrosphere system. Once released into the atmosphere, volcanic emissions rapidly undergo a complex series of chemical reactions. This thesis seeks to further the understanding of such processes by both observation and numerical modelling.
I have adapted WRF-Chem to model passive degassing from Mount Etna, the chemistry of its plume, and its influence on the wider atmosphere. This investigation considers model plumes from the point of emission up to a day’s travel from the vent and is able to reproduce observed phenomena of BrO formation and O3 depletion within volcanic plumes.
The model plume influences several atmospheric chemistry systems, including reactive nitrogen and organic chemistry. Plume chemistry is driven by sunlight, and I examine how the modelled phenomena identified in this investigation vary with the diurnal cycle.
In the modelled plume all of the bromine is involved in O3-destructive cycling. When HBr is exhausted, volcanic HCl sustains the cycling. The rate-limiting factor of this cycling, and therefore the rate of O3 destruction, is sunlight.
I find qualitative differences between the chemistry of low and high intensity plumes, with the bromine chemistry in the latter case being limited by O3 depletion.
This modelling investigation is complemented by an observational study of O3 in a young Etnean plume from which I estimate the rate of in-plume O3 destruction within seconds to minutes after emission.
These investigations demonstrate that volcanic plumes can be included in
complex, 3D atmospheric chemistry models, and that the output from these can
be used to observe and quantify influences of volcanic plumes on the wider
atmosphere.