Atmospheric reactions of ethers and ketones

Abstract

The atmospheric lifetimes of a series of ethers and ketones was established, with respect to reaction with O H radicals and Cl atoms, using a relative rate smog chamber technique. Reactivity of these compounds was affected by , their C - H bond dissociation energies, the oxygen atom in their structure, steric effects, and polarity contributions. From the rate constant data calculated in this work it was concluded that the tropospheric lifetimes of these compounds is primarily determined by their reactivity with O H radicals. Only four of the compounds analysed (2- chloro,1,1 ,1-trifluoro ethyl ethyl ether, Isoflurane, enflurane and acetone) had sufficiently long tropospheric lifetimes which will allow transportation of these species to the stratosphere. Three of these compounds were chlorinated ethers. These species may release their chlorine atoms in the stratosphere , ultimately resulting In ozone depletion . Release figures for the two halogenated an aesthetic ethers, isoflurane and enflurane , were calculated in our laboratory and combined with atmospheric lifetime data to establish the possible contribution of the anaesthetics to ozone depletion. It was estimated that only a fraction of the released species will be effective in causing ozone depletion. To establish the ulitlmate atmospheric fate of the anaesthetics , stratospheric photooxidation reaction mechanisms were investigated for these species. Result data indicated that the anaesthetics will undergo reaction processes initiated by chlorine atoms produced from the photodecomposition of the parent species. These chlorine-sensitised photooxidation reaction mechanisms ultimately lead to the formation of CF 20 and C02 , both greenhouse gases. Although the anaesthetics isoflurane and enflurane are released to the troposphere, their effect on stratospheric ozone and on world climate was estimated to be minimal compared with other CFCs. This work serves as a quick guide to the type of reaction processes which are important in environmental assessment of volatile anthropogenic species and also illustrates the significance of secondary factors such as emission figures, reaction products, etc., in atmospheric quality assessment