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The road to hell is paved with good intentions. Back in 1990, when we realized that chlorofluorocarbons (CFCs) were depleting stratospheric ozone, the countries of the world signed the Montreal Protocol to phase out their use. Hydrofluorocarbons (HFCs) were on the shelf as an alternative to CFCs. HFCs had much less effect on stratospheric ozone.
At the time, no one paid much attention to the fact that both CFCs and HFCs were a powerful addition to the Earth’s greenhouse warming. Both classes of compounds have a global warming potential that is often 1000 times greater than that of CO2.
But now with the implementation of the Paris Climate Agreement and an explosion of interest in air conditioning in India and the rest of the developing world, the increasing use of HFCs becomes of interest. It is estimated that nearly 700 million new air conditioners will be in place 15 years from now. This is big business and a big addition to the human-caused changes in our climate.
In mid-October, the countries of the world agreed to limit HFC emissions over the next 30 years, making a huge contribution to the eventual success of the Paris Climate Agreement. This is an agreement that cannot easily be undone by a different administration. Problem is: what are the alternatives to HFCs?
Some “natural” compounds, including isobutane, propane and propylene are potential substitutes, although these are flammable and a potential fire and explosion hazard. Years ago, refrigerators and air conditioners contained ammonia, which could be pulled back into service, despite its corrosive and toxic vapors. A promising new class of compounds includes hydrofluoroolefins, which are already in use in some cars and refrigerators.
Currently the choices for HFC replacement are not obvious, but the motivation should be enormous for innovative chemical engineers to supply compounds that work. The ideal substance will not harm our planet’s climate or its ozone layer and it will be non-toxic and non-reactive with a high heat capacity. Dow Chemical, Honeywell and other companies that now use HFCs all support the new limits, so they must have some good ideas in mind.
Let’s hope we can find something that works and test its environmental impacts before widespread implementation begins. With all chemicals introduced to our environment, science must rule.
Gonzalez, S., E. Jimenez, and J. Albaladejo. 2016. Assessment of the atmospheric loss processes initiated by OH radicals and sunlight and the radiative efficiency for a series of hydofluoroolefins, CF3(CF2)(x=1,3,5)CH = CH2. Chemosphere 151: 45-54.
Lunt, M.F. and 26 others. 2015. Reconciling reported and unreported HFC emissions with atmospheric observations. Proceedings of the National Academy of Sciences 112: 5927-5931.
Rigby, M. and 14 others. 2014. Recent and future trends in synthetic greenhouse gas radiative forcing. Geophysical Research Letters 41: 2623-2630.
Wuebbles, D.J., D. Wang, K.O. Patten, and S.C. Olsen. 2013. Analysis of new short-lived replacements for HFCs with large GWPs. Geophysical Research Letters 40: 4767-4771.