HFCs: Stratosphere, No Problem. Climate, Another Story.
by Bill Chameides | June 30th, 2009
posted by Erica Rowell (Editor)
Thanks to the Montreal Protocol, chemical coolants such as CFCs were replaced with alternatives that are less harmful to ozone, such as HFCs (hydrofluorocarbons). But HFCs, it turns out, are big global warmers. (Photo: ©James A Sugar / NASA)
Hydrofluorocarbons or HFCs have replaced those nasty Freons to protect the ozone layer, but those HFCs can still wreak climatic havoc.
Last week at the Goldschmidt conference in Davos, Switzerland, when I ran into V. Ramanathan, a leading climate scientist from the University of California at San Diego, I was reminded of two papers: the first paper I ever read by Ramanathan back in 1975 and a new paper I’d just read on the flight over, published in this month’s Proceedings of the National Academy of Sciences.
Way Back in ‘74: When the Chemistry of Atmospheric Ozone Was All the Rage
In 1974, fresh from my Ph.D., I headed out to the University of Michigan to do a post-doc with Ralph Cicerone. Those were heady times for the study of stratospheric ozone chemistry and I was fortunate to have parachuted into one of the hotbeds for stratospheric research. Just before my arrival, Ralph, Rich Stolarski, and Stacey Walters published a paper showing that chlorine atoms could deplete the stratospheric ozone layer.
Shortly after, Mario Molina and Sherry Rowland of the University of California at Irvine published the paper that would land them the 1995 Nobel Prize for Chemistry. Using laboratory measurements, atmospheric data, and the work of Cicerone et al., Molina and Rowland proposed that chlorofluorocarbons or CFCs, the chemicals then used in aerosol spray cans, refrigerators, and air conditioners, were depleting the stratospheric ozone layer. In short, CFCs were a global threat and we needed to stop using them.
In 1987, following the discovery of the ozone hole, the global community signed on to the Montreal Protocol — committing the world to a phaseout of ozone-depleting chemicals. And the hunt was on for a CFC replacement.
|NASA has been recording ozone values since 1979. This animation shows high concentration of ozone in red and low concentration of ozone (also known as the ozone hole) in purple. Notice that the ozone hole did not develop until the mid-1980s. (NASA)|
Replacing the Nasty CFCs
CFCs consist of carbon (C), fluorine (F) and chlorine (Cl). They work great as refrigerants and propellants, in part because they are very, very stable. But their stability is also their downfall. They are so stable that the only way they break down in the atmosphere is by penetrating into the stratosphere where ultraviolet sunlight breaks them apart, liberating chlorine atoms. The chlorine atoms, as per Cicerone et al., then attack the ozone that protects much of life below from that same ultraviolet light.
To protect the ozone layer, we needed chemicals that behaved like CFCs in some respects, so they could be used in refrigerators and air conditioners, but were less stable than CFCs so they would be broken apart before getting into the stratosphere. The first such compounds to come along were HCFCs, short for hydrochlorofluorocarbons, which have a hydrogen atom in addition to the C, F, and Cl. The hydrogen allows them to be broken down in the lower atmosphere, limiting the amount of chlorine that gets into the stratosphere.
But HCFCs still have chlorine and still deplete the ozone layer and so are not a permanent solution. In the Montreal Protocol they were listed as “transitional substitutes” to be phased out by 2020 in developed countries and 2040 in developing countries.
What comes after HCFCs? One candidate is HFCs, composed of H, C, and F but no Cl so they do not threaten stratospheric ozone. Other substitutes include carbon dioxide (CO2), ammonia, and various hydrocarbons. All things being equal, however, HFCs are more effective and would be the compounds of choice.
But all things are not equal, and that is where Ramanathan comes in.
HFCs and Global Warming
Return once again to mid-70s: Everyone is talking CFCs and stratospheric ozone depletion. And then along comes that paper (“Greenhouse Effect Due to Chlorofluorocarbons: Climatic Implications,” Science, 190: 50-52) by V. Ramanathan, then an obscure scientist from India. He pointed out that CFCs are also heat-trapping greenhouse gases. And very effective greenhouse gases at that — some 4,000–14,000 times more effective than CO2 on a 100-year time scale. (Source [pdf])
So getting rid of CFCs is a double win — it stops ozone depletion and prevents further global warming. Ditto for HCFCs (these compounds are about 100–2,300 times more potent than CO2 as a global warmer). But while HFCs are essentially safe for the stratosphere, they still act as greenhouse gases. How potent a greenhouse gas depends upon the specific HFC. One such compound, HFC-23 (CHF3), which is a by-product of HCFC-22 production, is 14,800 times more potent as a greenhouse gas then CO2. By comparison HCFC-22 is only 1,810 times more potent.
Do we need to worry about warming from HFCs? A new paper by Guus J. M. Velders of the Netherlands Environmental Assessment Agency and colleagues says we’d better.
According to their calculations under a “business as usual scenario” (i.e., without any regulations), global HFC production and emissions will increase rapidly in the coming decades, more rapidly than the emissions of CO2 and other greenhouse gases. By 2050, HFCs will have grown to 9-19 percent of the total emissions of CO2. If a global treaty stabilized CO2 at 450 ppm, but did nothing about HFCs, the contribution from HFCs would become 28-45 percent.
The large rise in HFC emissions reflects both the switch from HCFCs to HFCs and the large increase in the use of refrigerants and foaming agents in the developing world. In fact, the projections of Velders et al. indicate that by 2050 HFC emissions from developing countries could be eight times larger than that of developed countries.
New Replacements, New Treaty Needed
The good news is that the world does not have to follow a business-as-usual pathway. Businesses and countries just have to opt for alternatives to HFCs. That may happen. The European Union has already agreed to cap and reduce HFC emissions. The Waxman-Markey bill recently passed in the House also has specific provisions for HFC emissions. And a global treaty, on target to
be negotiated this December in Copenhagen, would very likely cap HFC emissions in the developed economies.
But the Velders paper clearly shows that the real determinant for HFCs will be in the developing world. A global treaty should include guarantees from the developing countries to keep their emissions of HFCs and other greenhouse gases significantly below business as usual trajectories in the next decade or two, and to accept a declining cap over the long-term. Well, that’s my opinion anyway.filed under: atmosphere, climate change, faculty, global warming, science
and: chlorofluorocarbons (CFCs), Hydrochlorofluorocarbons (HCFCs), Hydrofluorocarbons (HFCs), Montreal Protocol, ozone, ozone hole, paper, research