Aerosol Coupling in the Earth System (ACES)

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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 global 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 climate change. 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 sources usually represent the major input of organic material into the atmosphere. Some emitted organic compounds are known to be directly 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'. One by-product of these oxidation processes is the generation of involatile or highly soluble organic oxidation products which can contribute to the mass of airborne particles or 'aerosols'. Aerosols in the atmosphere have an important influence on visibility and climate, through the scattering and absorption of light and UV radiation, and can also have direct health implications because fine particles can be inhaled into the lung. The proposed work aims (i) to improve our understanding of the fundamental processes involved in the formation of aerosols from the chemical processing of natural hydrocarbons emitted from forested regions of the world: (ii) to assess the impact of those aerosols on atmospheric composition, climate and rainfall: and (iii) to assess the impact of changes in land use on the above processes and impacts. This will be achieved using a combination of experimental studies in laboratory chambers, observational studies in a tropical forested region, and assessment studies using numerical models of the atmosphere.