The ozone layer in the stratosphere is essential in protecting life on Earth from harmful UV irradiation. Small changes in ozone layer thickness can cause significant damage to human health and agriculture. Knowing the methods and causes for ozone depletion is therefore critical. Concerns that may impact the stratospheric ozone layer have emerged: explosive volcanic eruptions with significant halogen content, climate change and increased convection, and violations to the Montreal Protocol that limits the use of ozone depleting substances. Importantly, in the future, the largest perturbation to the ozone layer could be caused by volcanic eruptions. Explosive volcanic eruptions can alter stratospheric composition and chemistry, influencing the stratospheric ozone layer. The background composition of the stratosphere is central in determining the impact changes like a volcanic eruption will have on the chemistry and future composition. The widespread use of anthropogenic chlorine- and bromine-containing compounds through the emissions of chlorofluorocarbons (CFCs) and halons has been the cause of ozone depletion as observed over the polar regions as ozone holes. The Montreal Protocol and its amendments banning the CFCs and other ozone-depleting substances have been largely successful, but the long lifetimes of these compounds mean that full recovery of the ozone layer is still many decades away, and they are still present in the background stratosphere. Large explosive volcanic eruptions have the potential to alter the spatiotemporal profiles of the ozone column through changes in trace gas composition and aerosol loading of the stratosphere. Along with sulphur compounds, volcanic eruptions can inject halogens into the stratosphere, potentially leading to sudden and dramatic ozone losses on a hemispheric scale. This is a complex chemical system, involving heterogenous processes as well as gas-phase reactions varying with altitude.
The objectives of this project are to evaluate the impact on stratospheric composition, specifically ozone, from volcanic eruptions. Different chemical species can be injected into the stratosphere from volcanic eruptions and they have different impacts. Using 3-dimensional chemistry-climate modelling the impacts of halogen injection from volcanic eruptions into the stratosphere, the sensitivity toward latitude and season of the eruption in both contemporary and future climate scenarios will be elucidated. Originally the idea was to investigate the chemistry of selected Bromine species that are present in the atmosphere, using both laboratory and quantum chemical calculations of the central reactions, however, instead a new objective was to investigate the impact of novel sulphur chemistry on the formation of atmospheric aerosols using 3-diemnsional chemistry transport modelling. This objective builds on the knowledge gained in the outgoing part of the project and enables achieving a better understanding of the background tropospheric and stratospheric composition and impacts of changes.
