Emission Of CFC Replacements To The Atmosphere

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2/3/97 #12125 News Summary

EMISSION OF CHLOROFLUOROCARBON REPLACEMENTS TO THE ATMOSPHERE SHOULD BE LIMITED

Materials are also greenhouse gases

The hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) used to replace the chlorofluorocarbons (CFCs) banned by the Montreal Protocol have low or no potential to deplete ozone in the stratosphere, but they may contribute to climatic change, says Dr. Garry D. Hayman of the National Environmental Technology Centre in Oxfordshire, United Kingdom.

The presence of hydrogen in the HCFCs and HFCs means they potentially can contribute to ground-level smog formation just like other organic compounds. Hayman and Dr. Richard G. Derwent of the Meteorological Office in Berkshire have used a sophisticated numerical model to assess the contribution of selected HCFCs and HFCs. Their results appear in the February issue of Environmental Science & Technology, a monthly publication of the American Chemical Society.

Derwent has developed the photochemical ozone creation potential (POCP) to rank the contribution of individual compounds. Each compound in the list of CFC replacements has been indexed according to its ability to form ozone at ground level. The model calculations show that none of these compounds will contribute significantly to this problem, which confirms earlier expectations.

But Hayman and Derwent note that the HCFCs and HFCs are greenhouse gases. In combining their results with those of assessments undertaken by the World Meteorological Organization and the Intergovernmental Panel on Climate Change, they claim it is now possible to calculate the contribution that HCFCs and HFCs make separately to depletion of the stratospheric ozone layer, the formation of ground-level ozone and climate change. However, Hayman says, it is difficult to quantify the trade-offs that exist between the environmental ozone improvement and the climate change resulting from the use of HCFCs and HFCs. Therefore, Hayman maintains, "it would be prudent to ensure that emissions of these compounds to the atmosphere be kept as low as possible."

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