Hydroflourocarbons

Hydroflourocarbons (HFCs) are chemical compounds composed of hydrogen, fluorine, and carbon. Many industries widely adopted HFCs as replacements for chlorofluorocarbons (CFCs) after the international adoption of the 1978 Montreal Treaty, which required signatory nations to phase out their international use of ozonedepleting substances in order to prevent further damage to the Earth’s stratospheric ozone layer.

HFCs were found to be potent greenhouse gases (GHGs), however, and scientists raised concerns over their high global warming potential. Government and industry began to adopt a variety of voluntary and mandatory measures and collaborative efforts to reduce HFC emissions. Most significant is the 1997 Kyoto Protocol, which lists HFCs as among the six key GHGs targeted for international emissions reductions.

Most HFCs are odorless and colorless gases when at room temperature. Examples of HFCs include hexaflouropropane, pentaflouropropane, triflouromethane, tetraflouroethane, diflouromethane, and flouromethane. HFCs are commonly known through a standard numbering scheme. HFCs are a group of human-made industrial gases produced as byproducts of industrial manufacturing process. HFCs are not produced in nature. China, India, and Brazil are among the world’s leading producers of HFCs.

Concerns Over Ozone and Global Warming

HFCs rose to prominence in the late 20th century as scientific concerns over the Earth’s stratospheric ozone layer increased. The ozone layer provides the Earth’s surface with protection from damaging ultraviolet rays emitted by the sun. Scientific studies revealed that anthropogenic compounds such as chlorofluorocarbons (CFCs) and halons were depleting the ozone layer. The 1987 Montreal Protocol requires developed member nations to phase out the use of ozone-depleting substances by 2020 and requires developing nations to begin phasing out their use after 2012. The protocol also placed an international ban on the use of chlorofluorocarbons.

International agreements such as the Montreal Protocol concerning the ozone layer and national legislation such as the U.S. Clean Air Act provided a growing market for replacement substances such as HFCs. Various industries began to utilize HFCs as replacements for chloroflourocarbons (CFCs), hydrochloroflourocarbons (HCFCs), halons, and other ozone-depleting substances by the late 20th century. HFCs have an ozone-depletion potential of zero because they do not contain either of the known ozone-depleting substances chlorine or bromine.

HFCs were a popular industrial replacement for CFCs and other ozone-depleting substances because of their many benefits in addition to their ozone safety. The other benefits of HFCs include their low chemical reactivity, toxicity, and flammability; high level of energy efficiency and material compatibility; and ability to be recycled. These benefits made HFCs attractive to industries seeking to reduce their emissions of ozone-depleting substances. Some HFCs, however, have proven to be more difficult to work with and more expensive than their CFC counterparts.

Industrial applications for HFCs include refrigerants, air conditioning, solvent cleaning, aerosol propellants, and firefighting agents in fire-extinguishing systems. They are also used in the production of insulating foams such as food packaging, pharmaceuticals, nutraceuticals, flavors, and fragrances. Medical uses include propellants in newer models of metered dose inhalers used in the treatment of asthma. Refrigeration and airconditioning equipment and industrial aerosol propellants represent the largest industrial uses of HFCs.

HFCs raised concerns by the end of the 20th century, however, because of their high global warming potentials and growing rates of usage as other classes of substances were increasingly phased out under international agreements. HFCs are now classified as GHGs, which contribute to the greenhouse effect by partially trapping solar radiation before it can return to space, thereby raising the mean global temperature in a process known as global warming. As HFCs are entirely manufactured, they contribute to the anthropogenic or enhanced greenhouse effect. Although they currently represent a lower percentage on the scale of contributions to global warming, this percentage will rise, without future reductions in their usage.

Global warming potential is a numerical quantification of an individual chemical substance’s contribution to global warming in comparison to that of the same mass of carbon dioxide (CO2). Individual HFCs have a range of global warming potentials, with a typical range of between 1,000 and 3,000 times the global warming potential of CO2. Most HFCs have high global warming potentials, but they are lower than those of the CFCs they have largely replaced. HFCs also remain in the atmosphere for longer durations, even decades or more. Of all HFCs, HFC-23 is the most potent GHG, giving it the highest global warming potential.

HFC emissions released into the environment are entirely anthropogenic as there are no natural sources of HFC emissions. HFC emissions can occur at several stages, including fluid and product manufacturing, product use, and product disposal. Most HFC emissions occur at the source of application. HFC emissions can also be produced during the manufacture of other chemical substances. In the 1990s, HFC emissions totaled only trace amounts, but the figures have been steadily climbing in the 21st century.