The atmosphere is central to many of the environmental problems faced by society. Climate change, air quality degradation and ecosystem issues are all significantly impacted by atmospheric chemistry. Our understanding of atmospheric chemistry is driven by a variety of experimental types. Laboratory studies, studies in atmospheric chambers, short term field experiments and long term monitoring all provide insight into the processes controlling the composition of the atmosphere. Our understanding of all of these processes is integrated through the use of atmospheric models. These are sophisticated computer programs which quantify the processes going on in the atmosphere which allow prediction of the past, present and future state of the atmosphere. Professor Evans’ interests lie in the use of these models to better understand the atmosphere and thus improve our predictive capability of the composition of the atmosphere.
Professor Evans is also employed by the Composition Directorate within the National Centre for Atmospheric Science (NCAS)
Current research interests:
The emissions of reactive carbon (mainly in the form is isoprene C5H8) from the tropical rain forests represents a significant perturbation to the chemistry of the atmosphere. The atmospheric chemistry of C5H8 is complex and currently badly understood. Our studies have focused on the impact of C5H8 on compounds such as OH and HO2. We have used observations made by the FAAM BAe146 aircraft (the UK large research aircraft) over the rain-forests of Borneo to investigate the impact of isoprene on other compounds such as OH and HO2.
On average the planet is in darkness for 50% of the time. However, our previous studies of atmospheric chemistry have mainly revolved around daytime studies. Thus, our understanding of atmospheric chemistry during the night is limited. During the RONOCO flights over the UK night time chemistry was probed from the BAe146 research aircraft. Our modelling studies have investigated the night time chemistry and showed that the processes driving the chemistry at night are completely different to those during the day and our representation of the night time chemistry in models needs to be re-evaluated.
The atmosphere is composed of a gas phase with a suspension of liquid and solid phase aerosols. These aerosols offer a surface for reactions to occur on. These ‘heterogenous’ reactions have a significant impact on the composition of the atmosphere. The dominant route for this impact is through the reaction of N2O5 and HO2 on aerosol surfaces. Model simulations have been used to assess the impact of uncertainty about the rates of these reactions.
Pollution is emitted from the populated regions of the planet. Winds can blow the pollution across vast distances. This can lead to one part of the world causing air quality problems for another part. Air quality strategies for a region, needs to consider not only the impact of local policies but also the global scale. Understanding this global scale requires a firm understanding of the fundamental chemistry occurring in the atmosphere.
The ability of to measure the concentration of pollutants in the atmosphere has to be augmented with the capability to analyze the data. For example we have analyzed data to evaluate emissions from the mega-city of Lagos, or the processes destroying ozone in the Atlantic. Techniques such as Fourier analysis, Principal Components and Positive Matrix Factorization can all provide significant insights into the processes controlling the atmosphere.