Cooling Appliances Responsible for Global Warming

Large quantities of greenhouse gas ‘HFC’ released by fridges and air-conditioners every year. Altering the chemical structure of these substances could cut their atmospheric lifetime by decades.


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Arrival of Hydrofluorocarbons

Refrigeration and air-conditioning are the principal emitters of hydrofluorocarbons (HFCs). They were first manufactured in the 1990s, as substitutes for ozone depleting products, such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). 

While they do not deplete the ozone layer themselves, HFCs are potent greenhouse gases with high global warming potentials (GWP). These gases absorb infrared radiation from the Sun, trapping heat in the Earth’s atmosphere; contributing to the greenhouse effect. HFCs are retained in the atmosphere for, on average, 29 years.

Throughout manufacturing processes, from byproduct reactions, leakages to fridge deterioration, HFC substances are released. In an attempt to reduce certain emissions, methods were engineered to improve sealing systems. Yet, even with new technologies, the problem is still there; HFCs are still being expelled. 

While there is an increasing demand for air-conditioning, it’s important not to accumulate HFCs. Efforts have been put in place by the Montreal Protocol to regulate and eventually phase out these substances.

A Greener solution

Unsaturated HFCs, also called Hydrofluoroolefins (HFOs), are being adopted as alternatives, described as being ‘zero ozone depleting’ and having a low GWP.

The difference between a saturated and an unsaturated compound lies within their structure. A compound said to be saturated, has only single bonds linking carbon and hydrogen atoms, compared to multiple bonds between atoms in unsaturated compounds.

Diagram comparing a saturated and unsaturated molecule

This distinction seems relatively insignificant but has huge consequences on a molecule’s properties. Carbon-carbon double bonds (C=C) react more readily with hydroxyl radicals (OH, or oxygen-hydrogen) in the atmosphere. 

Saturated compounds earned their name because they resist addition reactions. In other words, radicals or molecules can’t add as easily. When a chain of carbon and hydrogen atoms only have single bonds linking them, that bond is essential to the structure, it can’t break away. Whereas if there are two bonds linking those atoms, one is more available to react with an exterior molecule – in this case a hydroxyl radical.

As they react quicker, unsaturated compounds have a shorter lifetime than saturated ones. Thus, HFOs exist in the atmosphere for a brief amount of time. This cuts an atmospheric lifetime of several decades for HFCs, to an estimated month for HFOs.

Fridges and air-conditioners are found in homes and shops all around the world. At the moment, many of these appliances are still transitioning to HFCs. Almost all HFCs have high global warming potentials. As we slowly phase out these substances, HFOs will be next in line. A deceitfully simple change in structure, makes HFOs a greener solution to the hazardous appliances we all have in our homes.


Sources:

D. J. Wuebbles, D. Wang, K. O. Patten, S. C. Olsen, Geophysical Research Letters, 2013, 40, 4767–4771, DOI:10.1002/grl.50908.

Atkinson, R., D. L. Baulch, R. A. Cox, J. N. Crowley, R. F. Hampson, R. G. Hynes, M. E. Jenkin, M. J. Rossi, J. Troe, and T. J. Wallington, Atmospheric Chemistry and Physics, 2008, 8, 4141–4496.

Bin Xiang,  Prabir K. Patra, Stephen A. Montzka, Scot M. Miller, James W. Elkins, Fred L. Moore, Elliot L. Atlas, Ben R. Miller, Ray F. Weiss, Ronald G. Prinn, S. C. Wofsya, Proceedings of the National Academy of Sciences of the Unites States of Amercia, 2014, 111, 17379-17384.

Y. Xu, D. Zaelke, G. J. M. Velders, V. Ramanathan, Atmospheric Chemistry and Physics, 2013, 13, 6083-6089. 

G. J.M.Velders, D. W.Fahey, J. S.Daniel, S. O.Andersen, M. McFarland, Atmospheric Environment, 2015, 123, 200-209.

IPCC/TEAP Special Report, 2005, https://www.ipcc.ch/site/assets/uploads/2018/03/sroc_spm-1.pdf

OzonAction, The Kigali Amendment to the Montreal Protocol: HFC Phase-down, 2016, https://wedocs.unep.org/bitstream/handle/20.500.11822/26589/HFC_Phasedown_EN.pdf?sequence=1&isAllowed=y

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