Atmospheric fate of dimethyl and fluorinated ethers

摘要

The purpose of the present study was to evaluate the environmental significance of dimethyl ether and the fluorinated ethers E143a (CH3OCF 3), E134 (CHF2OCHF2), E125 (CHF2OCF 3), and E216 (CF3OCF=CF2). Dimethyl ether is a proposed diesel fuel substitute. Concerns about mobile source emissions and their impact on urban tropospheric ozone formation have spurred research into alternative fuels. The fluorinated ethers are proposed CFC/HFC replacements in refrigeration applications. Attractive features of these ethers include the absence of chlorine and the incorporation of hydrogen, which will allow for degradation to begin in the troposphere.;Dimethyl ether has a short atmospheric lifetime of five days. Dimethyl ether degrades solely in the troposphere and will thus not impact stratospheric ozone. The short atmospheric lifetime and weak infrared absorption properties make dimethyl ether benign toward global climate. The atmospheric oxidation of dimethyl ether is predicted to result in the formation of methyl formate, formaldehyde, formic acid anhydride, and formic acid. E143a is dominated by the tropospheric degradation of hydroxyl radical having an atmospheric lifetime of less than 4.7 years. It is unlikely to interact with the ozone layer and has moderate global warming properties. E134 and E125 react slowly with tropospheric hydroxyl radical. E134 and E125 have lifetimes of 29.7 and 165 years with respect to OH loss, respectively. Both species will have substantial concentrations in the stratosphere and may be removed through reaction with O(1D). E125 is a severe global warming agent. The oxidation of E143a, E134, and E125 ultimately results in the formation of carbonyl fluoride, CF2O. E216 contains a double bond and thus undergoes a very fast hydroxyl radical addition reaction in the troposphere. E216 has a very short lifetime of 4 days and is thus neither a threat to stratospheric ozone nor a global warming agent. The incorporation of a double bond in a molecule represents a new molecular structure framework from which future CFC replacements can be generated.