Growth in stratospheric chlorine from short-lived chemicals not controlled by the Montreal Protocol.

We have developed a chemical mechanism describing the tropospheric degradation of chlorine containing very short-lived substances (VSLS). The scheme was included in a global atmospheric model and used to quantify the stratospheric injection of chlorine from anthropogenic VSLS ( ClyVSLS) between 2005 and 2013. By constraining the model with surface measurements of chloroform (CHCl ₃ ), dichloromethane (CH ₂ Cl ₂ ), tetrachloroethene (C ₂ Cl ₄ ), trichloroethene (C ₂ HCl ₃ ), and 1,2-dichloroethane (CH ₂ ClCH ₂ Cl), we infer a 2013 ClyVSLS mixing ratio of 123 parts per trillion (ppt). Stratospheric injection of source gases dominates this supply, accounting for ∼83% of the total. The remainder comes from VSLS-derived organic products, phosgene (COCl ₂ , 7%) and formyl chloride (CHClO, 2%), and also hydrogen chloride (HCl, 8%). Stratospheric ClyVSLS increased by ∼52% between 2005 and 2013, with a mean growth rate of 3.7 ppt Cl/yr. This increase is due to recent and ongoing growth in anthropogenic CH ₂ Cl ₂ -the most abundant chlorinated VSLS not controlled by the Montreal Protocol.