Climate impacts on tropospheric oxidation
Tropospheric methane (CH4) and ozone (O3) are the 2nd and 3rd most important climate gases after carbon dioxide (CO2). Tropospheric oxidation is responsible for removing CH4 from, and for controlling O3concentration in, the troposphere. Thus, understanding tropospheric oxidation is central to understanding our changing climate. Tropospheric oxidation chemistry is made up of chemical cycles linking the hydroxyl radical (OH) with the peroxy radicals (HO2/RO2), nitrogen oxide (NO) with nitrogen dioxide (NO2), organic compounds, halogens and aerosols. The interplay between these compounds has changed since the pre-industrial and is forecast to continue to change as the climate warms and the emission of air quality gases change.
Climate models are the primary tool to understand these changes, however, they tend to disagree over what tropospheric oxidation looked like in the past and what it will look like into the future (see for example Griffiths et al., 2021 or Stevenson et al., 2020). These differences are due to the differences in the physical (temperature, water vapour, clouds, solar radiation etc) and chemical (chemical mechanism, deposition, photolysis etc) representation of the model. However, quantifying how much each of these factors contributes to the differences seen between model oxidation is challenging, and thus far, diagnostics to understand these differences have been lacking.
The AerChemMIP project (one of the CMIP6 set of Model Intercomparison Projects) developed a set of chemical and physical diagnostics for climate model simulations run from the past into the. The results of these studies were used as part of the last AR6 IPCC report. This PhD project will start by analysing those outputs. This will focus on a combined analysis of changes in both O3 and OH concentrations and explore why the different models calculate different rates of oxidation. The analysis will bring together assessment of the different model representations of factors such as water vapour, UV radiation, emissions of chemicals into that atmosphere, and their deposition back to the ground to understand why models differ in their calculation of oxidants. The project will use an organic-bond centred perspective to provide an alternative method to consider model oxidation rates
A new AerChemMIP project has just started in preparation for the next IPCC report. The AerChemMIP2 project will deliver new climate model results and when these are available the PhD will turn to use these data and the additional model diagnostics they will contains to extend the analysis. Coupling this to the earlier work from AerChemMIP, will allow the PhD to make a comprehensive assessment of the processes leading to different rates of oxidation between different climate models so as to improve our assessment of how climate will impact atmospheric composition into the future.
The project will involve working with the climate modelling centres (UK Met Office, US NCAR, US NOAA, US GISS) to develop an understanding of their models and their characteristics. This may involve visiting these centres (or other institutions) to better understand their model and diagnostic approaches and for the student to develop new skills.
During the project student will develop skills in atmospheric chemistry, climate science, scientific computing and data processing. They will use the University of York’s Viking computer cluster for the analysis activities and will be provided with appropriate training. They may also need to use national facilities such as JASMIN, or ARCHER2. Python will likely be the dominant programming language, equipping the student will skills that can be transferred either within an academic setting or into an industrial / policy one.
As well as the support from the YES.DTN, student will form part of the Wolfson Atmospheric Chemistry Laboratories (WACL) cohort of students, and the wider cohort within the chemistry department at the University of York. Training will be provided both in-house within WACL, by the chemistry department and by the YES.DTN, which will cover both technical and soft skills. Where appropriate the student will attend other courses.
The project will be based around computational atmospheric chemistry but would be suitable for anybody with natural sciences (Chemistry, Physics, Biology), Maths, Engineering background etc. If you have queries about suitability or anything else to do with the project, please contact Prof. Mat Evans (mat.evans@york.ac.uk).