Hydrofluorocarbons lifetimes

Nimitz, J.S. and Skaggs, S.R. Estimating tropospheric lifetimes and ozone depletion potentials of one- and two-carbon hydrofluorocarbons and hydrochlorofluorocarbons, fJnvzron. Sci. TechnoL, 26(4) 739-744, 1992. 

Nimitz, J. S., and S. R. Skaggs, Estimating Tropospheric Lifetimes and Ozone-Depletion Potentials of One- and Two-Carbon Hydrofluorocarbons and Hydrochlorofluorocarbons, Environ. ScL Technol., 26, 739-744 (1992). 

Cooper, D.L., Cunningham, T.P., Allan, N.L., McCulloch, A. (1993) Potential CFC replacements Tropospheric lifetimes of C3 hydrofluorocarbons and hydrocarbons and hydrofluoroethers. Atmos. Environ. 27A, 117-119. 

An important outcome of this work has been the formulation of the ozone depletion potentials (ODPs) for chlorine-containing fluids. Arbitrarily. CFC-11 is assigned an ODP of unity the ODPs of other fluids are normalized to that of CFC-11 on a mass-for-mass basis. Important factors in determining the ODP of a fluid include its atmospheric lifetime and the quantity of chlorine it contains. Hydrochlorofluorocarbons (HCFCs) have much lower ODPs than CFCs—a consequence mainly of the former s lower atmospheric lifetimes. Hydrofluorocarbons (HFCs), which by definition contain no chlorine, have zero ODPs. 

International agreements (Montreal Protocol in 1987 and subsequent amendments), as well as national regulations, have strongly limited the production and the use of the CFCs. These chemical compounds have been gradually replaced by partially halogenated hydrocarbons, and specifically by hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). These alternative products are relatively easily destroyed in the troposphere and hence their lifetimes are substantially shorter than those of the CFCs (typically 1-10 yrs as opposed to 10-100 yrs). The ozone depletion potential of the HCFCs is about an order of magnitude smaller than that of the fully halogenated halocarbons. HFCs are not a threat to ozone because they do not contain any chlorine or bromine atoms. 

Chemists are creating substitutes for them that will retain their desirable properties, but will break down in the lower atmosphere so that they will not survive to reach the ozone layer. Most of the replacement compounds are being designed to contain C-H bonds, which increase the reactivity of the compounds and decrease their lifetime in the atmosphere. One solution to the problem is to replace CFCs with related compounds that contain no chlorine. Indeed, one of the most common replacements for CFCs is the family of hydrofluorocarbons (HFCs) such as 1,1,1,2,2-pentafluroethane (CF3CHF2). This class of compounds is less harmful to the ozone layer. 

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