Atmospheric chemistry and impacts of volatile and semi-volatile organic compounds: Fellowship extension application

The emission of trace materials into the atmosphere can have a variety of influences on the environment, ranging from immediate health impacts in the locality of the release to world-wide effects on atmospheric composition and climate. Organic compounds, such as hydrocarbons, are emitted in large quantities from both natural and human-influenced sources, and contribute to many of the well-publicised environmental phenomena, for example, photochemical smog and global warming. It is estimated that about 2 billion tonnes of organic material are emitted into the atmosphere each year. Natural sources include emissions from vegetation (e.g., forests), and such sources dominate when total global emissions are considered. Human-influenced emissions result from many sources, in particular road transport, distribution of petrol and other fuels, solvent usage and some industrial processes. In populated regions, such as the UK, emissions from such sources represent the major input of organic material into the atmosphere. Some emitted organic compounds (e.g. benzene, 1,3-butadiene and 'polycyclic aromatic hydrocarbons') are known to be detrimental to human health, for example as carcinogens. However, a much wider impact results from the chemical processing of organic material in the atmosphere, which leads to the generation of a variety of products, sometimes known as 'secondary pollutants'. Of particular importance is the generation of 'ozone', which is produced from the sunlight-initiated oxidation of volatile organic compounds (VOC) and nitrogen oxides (NOx). Ozone is a major component of photochemical smog, and is known to have adverse effects on human health, vegetation (e.g. crops) and materials. It is also a 'greenhouse gas' which contributes to global warming. Another by-product of these oxidation processes is the generation of involatile organic oxidation products which can contribute to the mass of airborne particles. Particulate matter in the atmosphere has an important influence on visibility and climate, through the scattering of light and UV radiation, and also has direct health implications because fine particles can be inhaled into the lung. The current fellowship programme set out to improve our knowledge and assessment of the quantitative impacts of organic material emitted into the atmosphere, and has made major advances in this area. These have been achieved by a combination of (i) laboratory studies of the oxidation of organic compounds, (ii) the development of highly detailed chemical mechanism (known as the 'Master Chemical Mechanism, MCM') which makes use of experimental data to build up an explicit description of how the organic compounds are oxidised and how the secondary pollutants (e.g. ozone, particulate) are formed, and (iii) the use of the chemical mechanism in models of the atmosphere to investigate the impacts of the organic compounds, and what can be done to reduce these impacts. The proposed fellowship extension aims to build upon this work by systematically developing a series of compatible chemical mechanisms of varying detail. These will range from an extended version of the MCM (which provides a detailed description of the chemistry, but which is most efficiently run in models with simple descriptions of air mass transport), through to highly simplified representations of atmospheric chemistry which can be applied efficiently in global models with sophisticated descriptions of air mass transport, such as the Meteorological Office's Unified Model (UM). In this way, the highly simplified chemistry will be traceable through to the MCM, and will be indirectly based on the results of experimental studies of atmospheric chemistry. This will allow improved confidence to be placed in the performance of such mechanisms (in terms of ozone and particulate formation) for the range of conditions appropriate to the lower atmosphere, and resulting from projected changes in emissions and climate.