Atmospheric chemical reactivity and ozone-forming potentials of potential CFC replacements

The Montreal Protocol will lead to the eventual phaseout of the production of chlorofluorocarbons (CFCs) and other halogenated organic compounds that are implicated in the depletion of stratospheric ozone. Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) have been developed as potential ''in-kind'' replacement compounds. To ensure that these compounds are acceptable, industry and regulatory agencies are assessing the safety, toxicology, and environmental impact of the HCFCs and HFCs before widespread production is commenced. One of the environmental issues concerns the contribution that the HCFCs and HFCs make to photochemical ozone production. Photochemical ozone creation potentials (POCPs) have been calculated using a photochemical trajectory model. The POCPs of the HCFCs and HFCs are low, indicating that these compounds do not have a large potential to contribute to ground-level ozone formation. This results from their low reactivity compared to the other, more reactive, organic compounds present during a photochemical episode. HCFCs and HFCs also contribute to stratospheric ozone depletion and climate change. While the relative importance of the compounds within these issues can be defined with some certainty, our understanding of how to weigh the relative importance of the different issues is not sufficiently well developed to assess with any degree of certainty the benefits or the harm that might result from switching to the use of HCFCs and HFCs.