Atmospheric Impacts of Criegee Biradical Chemistry

Poor air quality costs the UK in excess of £20billion per year. This poor air quality is controlled by the chemical composition of the atmosphere, and the interactions between the multitude of different chemical species in the atmosphere. These interactions are typically mediated by highly reactive trace gas species, leading to chemical transformations which control not only air quality but also ozone depletion and climate change. Our understanding of the vast array of chemical compounds and their transformations in the atmosphere dictates our ability to understand, predict, and address these environmental problems.

For many years, one class of trace species known as Criegee biradicals have been theorised to participate in chemical transformations in the atmosphere, both in regions dominated by natural processes and in those influenced by man. Owing to their high reactivity and transient nature, Criegee biradicals have proven difficult to measure directly, leading to large uncertainties in their chemistry and their impacts on atmospheric composition.

Recent ground-breaking experiments led to the first direct observations of Criegee biradicals, and showed them to be much more reactive than previously anticipated on the basis of indirect measurements and theoretical calculations. The simplest Criegee biradical (CH2OO) was shown to react with sulfur dioxide (SO2) 1000 times faster than previously expected, potentially revealing a previously unknown route for production of sulfur trioxide (SO3) in the atmosphere and impacting our understanding of atmospheric production of sulfuric acid, acid rain and sulfate aerosol, with implications for both air quality and climate change. However, these experiments were performed at low pressures (less than 1 % of atmospheric pressure), and the reaction rate and products at higher pressures relevant to the atmosphere may be different to those observed in the low pressure experiments. Assessment of the atmospheric impacts of a reaction requires knowledge of both the rate of the reaction and the product yields.

This work will take advantage of the new opportunities to explore the chemistry and impacts of Criegee biradicals in the atmosphere, using techniques which will enable investigation of both reaction rates and product yields at temperatures and pressures relevant to the atmosphere. Initial experiments will be performed with existing experimental apparatus in the School of Chemistry at the University of Leeds. Subsequent experiments, in collaboration with project partners at the Sandia National Laboratory in California, will develop novel instrumentation to monitor Criegee biradicals and their reaction products at atmospheric temperatures and pressures under idealised conditions in the laboratory. The instrumentation developed during the fellowship will be applied to measurements of Criegee biradicals in more complex systems in an atmospheric reaction chamber in Leeds, and has the potential for future development to field measurements of Criegee biradicals in the atmosphere.

Atmospheric impacts of experimental results obtained in this work will be assessed through the use of detailed numerical models of the atmosphere, in collaboration with world-leading research groups at the University of York and the Massachusetts Institute of Technology (MIT).

This fellowship will generate results of interest to groups involved in research requiring accurate simulation of atmospheric composition, including those involved in interpretation and simulation of field data, forecasting air quality, determination of aerosol production rates and impacts of aerosols on air quality and climate. The results will be of interest to both academic groups and those in government agencies such as DEFRA, the Department of Health and the Environment Agency who use atmospheric models for future chemistry and climate simulations in order to inform policy and direct air pollution abatement strategies (see letter of support from Prof. Timmis, Environment Agency).

The experimental techniques developed will be of interest to groups with an interest in the measurement of trace species in the gas phase, including not only atmospheric scientists but also those involved in experimental studies of astrochemistry, heterogeneous catalysis, the use of deposition processes in materials synthesis and those involved in the development of gas phase measurements for medical diagnostics.

Results will be communicated to the interested parties in a number of ways, as outlined in the 'Pathways to Impact'. Primary research results will be disseminated through peer-reviewed journals such as Atmospheric Chemistry and Physics, Geophysical Research Letters and the Journal of Geophysical Research. The large potential impact of the results of this fellowship lends itself to publication in high impact journals such as Science and Nature. I anticipate publishing several articles per year for each of the five years of the fellowship.

I propose to present results at international conferences, such as the European Geosciences Union (EGU), American Geophysical Union (AGU), Royal Society of Chemistry Gas Kinetics Symposia, Atmospheric Chemical Mechanisms (ACM) and the International GEOS-Chem user group meetings. I will also give seminars at universities with active research programmes in atmospheric science, with seminars given at the project partner institute fostering opportunities for knowledge exchange and further collaboration.

Results from the fellowship will be made available through the Master Chemical Mechanism (MCM) and GEOS-Chem websites in a format appropriate for use in atmospheric models, and a dedicated website will be developed to highlight results.

A workshop will be held during the project to discuss results from this work with research groups interested in Criegee biradical chemistry and its impacts on atmospheric composition. The workshop will provide an opportunity to place the results of this work in the context of those from other world leading research groups, enabling discussion of further work and potential future collaborations.

Potential applications of novel instrumentation developed in this work, and opportunities for knowledge exchange, will be investigated through attendance at conferences and seminars in research areas requiring measurements of trace gas species. This will provide opportunities to showcase the techniques developed in this work, and to learn from other scientists using similar techniques in other fields.

Engagement with science journalists from widely read newspapers and periodicals will be possible through the press office at the University of Leeds, and I will take advantage of courses in writing for the media and public presentation offered by the university and run by professional journalists.

Interaction with the public will be achieved through discussion events at the Leeds Festival of Science and the Leeds branch of Café Scientifique. Public outreach and widening participation events organised by the School of Chemistry in Leeds will provide opportunities to generate interest in atmospheric science in the wider community and to introduce the public to the application of science and scientific techniques to societal problems.