Atmospheric Fate of Unsaturated Ethers

摘要

Oxygenated volatile organic compounds form a major component of the trace gases found in the troposphere (Singh et al., 2001). They are emitted directly into the atmosphere from biogenic sources, solvent and fuel additives use and are also formed in the tropospheric oxidation of all hydrocarbons. A number of oxygenated compounds are used as alternatives to aromatic and halocarbon solvents both in terms of toxicity problems and in the case of aromatic compounds as a means of reducing the levels of oxidant formation in the troposphere. It is apparent that oxygenated compounds will thus play an increasing role in determining the oxidising capacity of the troposphere both on a regional and global scale. The degradation of oxygenated volatile organic compounds in the troposphere leads to the production of a range of secondary pollutants such as ozone, nitrates and secondary organic aerosols. Ozone formation is of particular concern since it is known to have adverse effects on human health, vegetation and a variety of materials, and it is also a greenhouse gas. Indeed, strategies for the control of emissions of volatile organic compounds have been based on their individual contribution to the photochemical formation of ozone (Derwent et al., 1996). Information on the fate of oxygenated compounds in the troposphere is not only important in terms of oxidant formation, but oxidation of simple oxygenated compounds often leads to the generation of poly-functionalized species. These compounds can be of low reactivity in the gas phase and thus their relatively high solubility and low vapour pressures may lead to uptake in cloud and fog droplets or to formation of secondary organic aerosols. Hence, anthropogenic emissions of oxygenates may impact on wet deposition and also on climate by increasing the levels of tropospheric aerosol.