Australasian Science Magazine

For the past 3 years there have been efforts to list under the Montreal Protocol a group of substances that replace the CFCs and HCFCs but do not contain chlorine and therefore cannot harm the ozone layer. Credit: iStockphoto

By Ian D. Rae

Ozone-depleting chemicals may have been phased out under the Montreal Protocol, but the global warming potential of their replacements is thousands of times greater than carbon dioxide.

In September the world celebrated the 25th anniversary of the Montreal Protocol, which controls and phases out substances that deplete the ozone layer. The Protocol is the operative arm of the Vienna Convention for the Protection of the Ozone Layer, and every country in the world has signed and ratified it. As a country close to the springtime Antarctic ozone hole (http://ozonewatch.gsfc.nasa.gov/), and a good global citizen, Australia has put a lot of effort into the development and implementation of this multinational environment agreement.

The Earth’s ozone layer, which protects us from harmful ultraviolet radiation, has been under threat from chlorine atoms released by chlorofluorocarbons (CFCs) and related anthropogenic chemicals. The CFCs are almost gone now, and the Protocol has in place a phase-out schedule for their successors, the hydrochlorofluorocarbons (HCFCs), the most common of which in our daily lives is HCFC-22 (chlorodifluoromethane) which is the working fluid in home air conditioners. Other ozone-depleters being phased out under the Montreal Protocol are the halons, which are used in fire protection, and the fumigant methyl bromide.

If all countries stay on-track, the ozone layer will recover by the middle of this century. So what’s next for the world’s most successful multinational environment agreement?

Changing the Montreal Protocol?

For the past 3 years there have been efforts to list under the Montreal Protocol a group of substances that replace the CFCs and HCFCs but do not contain chlorine and therefore cannot harm the ozone layer. These are the hydrofluorocarbons (HFCs). A prominent member of this family, HFC-134a (tetrafluoroethane), is the working fluid in most of our automobile air conditioners and many of our refrigerators.

In developing countries, the use of HFCs is increasing as the ozone-depleters are phased out. While the HFCs are not ozone depleters, they have significant global warming potential and could soon make up a significant proportion of greenhouse gas emissions. The “controlled substances” – CFCs and HCFCs – are also global warmers, and it has been calculated that phasing them out under the Montreal Protocol has done more to protect the climate than actions taken under the Kyoto Protocol.

Most of us think about the Kyoto Protocol, which was derived from the United Nations Framework Convention on Climate Change, in terms of carbon dioxide emissions but it also includes a basket of gases, among them HFCs and other substances, that have much higher global warming potential than CO2.

There have been proposals to include HFCs in the Montreal Protocol and organise a phase-down of their production and use, but the signatory countries have been unable to reach consensus on this step. Proponents argue that because HFCs are used in similar applications to the ozone-depleting CFCs and HCFCs, the Montreal Protocol’s mechanisms for agreeing on production and consumption (and, incidentally, emissions) could be easily extended to the HFCs. Moreover, they claim, the Protocol and its parent, the Vienna Convention, both include expressions of concern about climate effects that could warrant the inclusion of non-ozone-depleting substances.

Opponents say that this is an over-interpretation of sections of both the Protocol and the Convention in which the possible climate impacts of ozone depletion are mentioned. Furthermore, they say, developing countries have enough to cope with under present phase-out schedules and cannot accept the extra responsibilities for managing HFCs.

At the moment it’s a stalemate. Amendments to the Montreal Protocol have been proposed by some Pacific Island states that have local concerns about sea level rise (as do some African states), and by the Canada–US–Mexico consortium which is doing most of the heavy lifting. Opposing the amendments are India, China and Brazil, along with other developing countries.

Using the Montreal Protocol to control HFCs makes practical sense. However, adding HFCs to the Protocol may require more extensive changes than just creating a new category of substances of concern. International agreements like the Montreal Protocol are thrashed out line-by-line before consensus is reached and everybody heaves a sigh of relief. The Montreal Protocol has been amended from time to time over the years, but unless something remarkable and unexpected happens it is unlikely that anything like the current proposals will be accepted in the short term.

A possible approach to dealing with HFCs, along with perfluoro­carbons and other industrial chemicals with significant global warming potential like sulfur hexafluoride, might be to add a Montreal Protocol-like regime to the Kyoto Protocol as negotiations for its extension take place over the next few years. However, negotiations in that forum are also slow, and there might also be resistance to moving from the present market-based mechanism to a regulatory regime.

Another Way: Changing the Chemicals

The threat that a chemical substance might be banned or its uses restricted on health or environmental grounds always creates a business opportunity. Companies already possessed of alternative products come to the fore, and others put their industrial chemists to work to make new substances that will do the job but not create problems.

In the first category we have seen the rise of the “natural refrigerants” movement, consisting of manufacturers and environmental advocates who champion substances like ammonia, carbon dioxide and simple hydrocarbons like propane and isobutane.

Ammonia was once a popular refrigerant but its inflammability led to several serious fires in the 1930s and it was an easy target for manufacturers of the new CFCs and HCFCs. Ammonia is also quite toxic, and in its re­incarnation it is only used in chillers placed outside buildings, cooling the inside space by means of a loop of heat transfer fluid.

Carbon dioxide can also be used in chillers, and it is ironic that the iconic greenhouse gas is replacing chemicals with higher global warming potentials. CO2 was also touted for auto air conditioning in Europe, but the necessary engineering to contain the higher pressures involved would have made it too expensive so the idea was abandoned.

There are other approaches that involve the production of substances that have low global warming potential because, should they ever be released into the environment, they are rapidly destroyed in the lower atmosphere. This vulnerability is achieved by building in some “weak links” – points where the molecules are attacked by reactive oxygen species in the atmosphere. The new gases still have to meet the usual criteria – suitable boiling point and other physico-chemical properties, stability in service, low or moderate cost of production, toxicity, and low flammability – as well as being readily degradable.

Chemists working for the US fluorocarbon manufacturers, Du Pont and Honeywell, have achieved this and are now producing what they call hydrofluoroolefins (HFOs). The weak link in the two products produced so far is a carbon–carbon double bond that makes the molecules vulnerable to atmospheric oxidation. Du Pont’s Opteon™ yf is coming into use for automobile air conditioning in the United States and the European Union. It is a three-carbon molecule with four fluorines.

In another application, fluorocarbon gases have been used for many years to froth up molten polyurethane and polystyrene plastics so they can be extruded as foams that solidify with the gases trapped in the bubbles. Polyurethane foams are used in mattresses and furniture upholstery, while polystyrene foams are used in insulating panels, packaging and cups for hot beverages.

In the production of these materials, the ozone-depleting and global warming gases are being replaced by low-boiling hydrocarbons such as pentanes and butanes, and with a range of oxygen-containing molecules such as ethers and esters, all of which have low global warming potentials. These substances are more flammable than the fluorocarbons they replace, so greater caution is needed in their use.

Addressing this issue, Honeywell has introduced the fluorocarbon HFO-1234ze (a chemical isomer of the Du Pont product) that has low flammability but is more expensive than the other alternatives.

Introducing a range of new climate-friendly chemicals to replace HFCs and HCFCs could ease the pressure to alter either the Montreal or the Kyoto Protocol. If some of them are more expensive than those they replace – and that is the situation at present although costs could come down as production increases – then it’s a price we may have to pay for climate protection.