Article

Chemical lifetimes of chlorinated aliphatic priority pollutants in the Canadian troposphere

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Abstract

Estimates have been obtained for all half-lives of several chlorinated aliphatic pollutants in the Canadian troposphere. The rates of reaction are strongly dependent on the magnitude of the second-order rate constant for reaction of the pollutant with OH, and on the intensity of solar radiation , which is determined both by season and geographical location. Of the pollutants studied, trichloroethylene has the shortest half-life of 2–5 days in summer, depending on location. Dichloromethane, 1,2-dichloroethane and tetrachloroethylene are each about one order of magnitude longer lived than trichloroethylene; 1,1,1-trichloroethane and 1,1,2,2-tetrachloroethane are about two orders of magnitude longer lived than trichloroethylene. Under urban conditions, high rates of oxidation, and hence short half-lives, are favoured by high tropospheric concentrations of ozone and low concentrations of NO2. With the exception of 1,1,1-trichloroethane, none of these substances is predicted to pose a significants threat to stratospheric ozone.

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... Deposition is the main route of transfer of atmospheric pollutants from air to other environmental compartments. It can lead to contamination of groundwater, soil and vegetation and hence lakes, rivers and the sea (Philp, 1995 Bunce and Schneider (1994) to screen persistent chlorinated aliphatic compounds in rural and urban atmospheres. The T 1/2 of compounds was estimated by using mathematical models that take into consideration photolysis and/or reaction with OH radicals. ...
... Once in the atmosphere TCE reacts with photochemically produced 355 hydroxyl radicals. Due to this process TCE shows half-life times of a few days (Brunce and Schneider 1994). The major products of atmospheric oxidation were dichloroacetyl chloride, formyl chloride and phosgene (Christiansen and Francisco 2010), the latter being very toxic. ...
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