Dr Ryan Hossaini

Reader in Atmospheric Chemistry

Research Interests

Ryan's research examines long-term changes in the chemistry and composition of Earth’s atmosphere and how such changes may influence climate, air quality and the ozone layer. This involves the development and application of state-of-the-art numerical models, run on supercomputers, which simulate the past, present and future state of the atmosphere. His recent work has focussed on:
  • Ozone-Depleting Substances (ODSs) and Ozone Layer Recovery. Despite production of many long-lived ODSs (e.g. CFCs) being controlled by the UN Montreal Protocol and its amendments, ozone depletion remains a persistent environmental issue. Our research examines trends in the atmospheric abundance and impacts of so-called Very Short-Lived Substances (VSLS) – a class of ODSs not controlled by the Protocol – whose emissions have been increasing in recent years. Our recent work has highlighted the increasing threat to stratospheric ozone from anthropogenic VSLS emissions, particularly from Asia. See also our recent Nature reviews on ODSs and ozone layer recovery.
  • Ozone Chemistry-Climate Interactions. In the stratosphere, ozone prevents damaging levels of UV radiation reaching Earth’s surface. Ozone also absorbs terrestrial IR radiation and is therefore a greenhouse gas. Changes in can ozone exert a significant and complex influence on climate. This research seeks to understand chemical drives of ozone changes, particularly in the climate-relevant upper troposphere/lower stratosphere, and the radiative implications. See our recent Nature Geoscience paper on the efficiency of halogenated VSLS at influencing climate through ozone loss in the lower stratosphere.
  • Tropospheric Halogens and Atmospheric Oxidising Power. Halogen chemistry is infamous for its role in stratospheric ozone layer depletion. However, there is growing evidence reactive halogens (iodine, bromine and chlorine) also exert significant influence on tropospheric composition. For example, chlorine atoms are highly reactive and are a potentially important tropospheric oxidant, influencing the lifetime of greenhouse gases (e.g. methane) and volatile organic compounds. However, the tropospheric abundance and trends of chlorine atoms, along with other halogens, is very poorly known. Our work seeks to understand the processes governing the release and recycling of halogens from the biosphere and to quantify their direct and indirect impacts on the troposphere's oxididing power, using models (e.g. see here and here).

  • UK Air Quality. Elevated ground-level ozone in recent hot summers and during heatwaves has raised concern that climate change could exacerbate ozone air pollution in the UK. We are building statistical models and applying downscaling techniques to better understand the relationship between ozone and meteorological covariates and to provide more skilful forecasts of extreme ozone events.

  • Data-Driven Clustering Methods for Climate Science. This work is supported by the EPSRC to explore the use of clustering in the analysis of large climate model datasets from model intercomparison projects. Our recent work has shown that clustering can potentially provide powerful insight into such data, and may help characterise areas of uncertainty across models.