The US Environmental Protection Agency (EPA) was directed by President Bill Clinton to press ahead with its controls on HFCs in his Climate Change Action Plan, published in mid-October. A week later, EPA officials created a stir at a conference on CFC alternatives in Washington by advising potential users of HFCs to be aware of their global warming potentials (GWPs) before buying.
HFCs do not contain chlorine or bromine and are therefore not ozone depleters. They are mostly being marketed as refrigerants. HFC-134a in particular is being sold as a CFC replacement in supermarket refrigerators. But one, HFC-152a, is being sold for use as a foam-blowing agent and aerosol propellant.
HFCs are, however, greenhouse gases of varying potency, and as such they are subject to the UN Convention on Climate Change, signed at last year's Earth Summit. Countries ratifying the treaty become committed to returning their greenhouse gas emissions to 1990 levels by 2000.
The Department of the Environment (DoE) in the UK acknowledges that the global warming potentials (GWPs) of HFCs will need to be tackled in the national strategy on greenhouse gases. This is due to be completed around the end of 1993, satisfying one of the UK's obligations under the Convention.
The UK is in a trickier position than the USA because it has chosen to interpret the Convention as requiring emissions of each individual greenhouse gas to be returned to 1990 levels by 2000. Because HFCs were not being produced in any significant quantity in 1990, strictly speaking their emissions should therefore be prohibited. The USA does not have this dilemma because it has chosen to apply the Convention target to all greenhouse gases as a "basket".
However, the DoE says it is keen for CFC users to switch to alternatives as quickly as possible and will therefore not ban HFCs. But it is now considering whether to issue recommendations or introduce controls on HFCs to ensure they are not used frivolously. It will keep an eye on developments in the USA before deciding how to proceed.
In May, the EPA issued a notice of proposed rule-making outlining plans to restrict the use of high-GWP chemicals to "high value" uses and impose conditions of use. It is now carrying out risk assessments which will include an evaluation of their contribution to global warming and ground-level ozone formation. Details of the limitations to be imposed will emerge next February and the regulations will be expanded with experience.
Also in the President's action plan is a direction to EPA to enter into voluntary product stewardship agreements with producers of HFCs with long atmospheric lifetimes. This is designed to ensure that companies "commit to not selling those chemicals for emissive uses and that users of long lived gases handle the material in an environmentally responsible manner - by capturing and destroying the gas rather than emitting it into the atmosphere."
Environmentalists are sceptical of the voluntary aspects of the action plan but say the regulatory measures are likely to prove valuable.
HFC manufacturers are keeping a close watch on the EPA's deliberations in order to ensure that it takes into account aspects such as the atmospheric lifetimes of the chemicals and the total equivalent warming impact (TEWI) of equipment - a measure of the direct warming impact associated with HFC releases combined with the indirect effect of carbon dioxide emitted in producing energy to run the equipment.
The HFCs which appear most vulnerable to restriction are 125 and 143a. According to the EPA, these have GWPs about 3,500 times greater than CO2 over a 100-year time span. If used in a 55%/45% blend in supermarket refrigeration, the direct warming effect caused by emissions of these two chemicals would amount to 76% of the total, with indirect emissions accounting for only 24%.
The HFC with the smallest GWP is 152a. Du Pont intends to sell this to an emissive use, but points out that it has an atmospheric lifetime of only two years.
Between these extremes lie HFCs-134a and 32. According to the EPA, these have GWPs of about 600 and 1,200, respectively, relative to that of CO2 over a 100-year time span. ICI produces both on a commercial scale, and says that considerations of GWP have led it to prefer the use of HFC-32 over 143a in blends as replacements for CFC refrigerants. The company says it is also working with customers to minimise leaks from equipment and to maximise the energy efficiency of the equipment.
ICI says it also regards as a high priority reductions in emissions of HFC-23 - a by-product of the manufacture of HCFC-22, an ozone-depleting substitute for the CFCs which also has a relatively high GWP of about 1,600 relative to that of CO2. ICI produces the chemical at Runcorn in Cheshire. The EPA also intends to address this emission source by means of voluntary programmes.