Phosgene in the stratosphere

An understanding of the sources and ensuing reactions of chlorine-containing compounds in the stratosphere is essential for the evaluation of their impact on the ozone layer. Whilst phosgene should be largely removed in the troposphere, it is anticipated that oniy slow photolysis will occur in the stratosphere. 

The two most probable loss processes of phosgene in the stratosphere are photolysis, and transport into the troposphere. Phosgene can be formed in situ in the stratosphere [36a], and indeed it is one of the main photo-oxidation products in the upper troposphere and lower stratosphere from the breakdown of chlorinated hydrocarbons (of both natural and anthropogenic origin). For example, the relatively inert tetrachloromethane accumulates in the air, but can photodissociate in the stratosphere according to  

Abstraction of a hydrogen atom from the trichloromethane molecule by [OH] radicals results in the formation of a [CClj]- radical, which reacts with dioxygen to form phosgene and [CIO]- [36a,1926a], This process is considered to occur in those regions of the atmosphere where there is iittle ozone available for destruction, so that before ozone is properiy encountered the [CIO]- wiil be reduced to C1-, which will be converted to HCl by abstracting a hydrogen atom from, say, methane. Less is understood about the fate of the 

Phosgene is the main oxidation product of dichloromethane, resulting from the abstraction of the molecule s two hydrogen atoms. Further photolysis could lead to chlorine atoms being produced in the atmosphere [36a, 1926a], Further research in this area is clearly warranted. 

It is anticipated that further environmental research will lead to a satisfactory resolution of the seemingly conflicting statements in the literature concerning the effect of phosgene on the ozone layer. 

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