The Cycle of Tropospheric Phosgene

Abstract

Phosgene (COCl₂) is produced in the earth’s atmosphere from the degradation of a variety of chlorinated compounds including tetrachloroethylene (C₂Cl₄), trichloroethylene (C₂HCl₃), chloroform (CHCl₃), methylchloroform (CH₃CCl₃), and carbon tetrachloride (CCl₄). These chlorinated compounds fall into two generic reactivity classes: 1. Tetrachloroethylene, trichloroethylene, chloroform., methylchloroform, the four reactive phosgene parent compounds (referred to here as the RPP compounds) that are primarily destroyed in the troposphere by reaction with OH; and 2. Carbon tetrachloride which is unreactive in the troposphere and is destroyed primarily by photolysis in the stratosphere. Thus the degradation of the RPP compounds lead to the production of tropospheric phosgene, while CCl₄ and to some extent also the RPP compounds leads to the production of stratospheric phosgene. Tropospheric phosgene is in turn believed to be removed from the atmosphere by rainout and ocean deposition (Singh, 1976), while stratospheric phosgene is thought to be destroyed by photolysis (Crutzen et al., 1978).