Atmospheric Impacts of Criegee Biradical Chemistry

点击翻译按钮获取中文摘要

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).