Hydrofluorocarbons

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Hydrofluorocarbons

Introduction

Hydrofluorocarbons (HFCs) are an alternative to chlorofluorocarbons (CFCs), halons, and other ozone-depleting substances. They are used in various applications, especially refrigeration, as a substitute for these substances. Although HFCs have been an effective part of the solution to ozone depletion, they are becoming an increasing global warming concern. As a greenhouse gas, and one with a high global-warming potential, increasing HFC emissions are a significant global concern.

Historical Background and Scientific Foundations

In 1974, scientific research emerged showing that CFCs were causing depletion of the ozone layer. In the years following, international action began to reduce emissions of ozone-depleting substances, especially CFCs. On January 1, 1989, the Montreal Protocol on Substances that Deplete the Ozone Layer went into effect. After an amendment, the international retreat required elimination of the production and use of CFCs and other ozone-depleting substances by 1996.

The elimination of CFCs created a demand for alternatives. HFCs are a substitute for CFCs, with the difference being that a fluorine atom is present in place of the chlorine atom. Although some HFCs can cause ozone depletion, it occurs at much lower levels, and most HFCs used in industry have no ozone-depleting effects.

Impacts and Issues

HFCs have replaced CFCs and halons for a range of applications and are used in refrigeration, air conditioning, aerosols, and fire extinguishers. The increased use of

HFCs has resulted in HFC emissions increasing by more than 250% from 1990 to 2005.

The major controversy associated with the increased use of HFCs is that they are a greenhouse gas and so contribute to global warming. HFCs are one of the six greenhouse gases targeted by the Kyoto Protocol. In 2005, HFCs accounted for 1.7% of greenhouse emissions by the United States.

WORDS TO KNOW

CHLOROFLUOROCARBONS: Members of the larger group of compounds termed halocarbons. All halocarbons contain carbon and halons (chlorine, fluorine, or bromine). When released into the atmosphere, CFCs and other halocarbons deplete the ozone layer and have high global warming potential.

GREENHOUSE GASES: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth's surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth's atmosphere, causing global warming and global climate change.

HALONS: A class of compounds, also called bromofluorocarbons, that contain bromine, chlorine, and carbon or fluorine. Used as fire retardants in fire-extinguishing systems. Potent greenhouse gases with high ozone-depletion potential.

KYOTO PROTOCOL: Extension in 1997 of the 1992 United Nations Framework Convention on Climate Change (UNFCCC), an international treaty signed by almost all countries with the goal of mitigating climate change. The United States, as of early 2008, was the only industrialized country to have not ratified the Kyoto Protocol, which is due to be replaced by an improved and updated agreement starting in 2012.

OZONE LAYER: The layer of ozone that begins approximately 9 mi (15 km) above Earth and thins to an almost negligible amount at about 31 mi (50 km) and shields Earth from harmful ultra-violet radiation from the sun. The highest natural concentration of ozone (approximately 10 parts per million by volume) occurs in the stratosphere at approximately 15.5 mi (25 km) above Earth. The stratospheric ozone concentration changes throughout the year as stratospheric circulation changes with the seasons. Natural events such as volcanoes and solar flares can produce changes in ozone concentration, but man-made changes are of the greatest concern.

HFCs are of higher concern than other greenhouse gases because they have high global warming potentials of between 140 and 11,700, meaning that they trap from 140 to 11,700 times more heat per gram than carbon dioxide. With the increased use of HFCs, it is expected that emissions will continue to increase and to become a greater proportion of total greenhouse gas emissions. As this occurs, the use of HFCs is expected to come under greater scrutiny.

BIBLIOGRAPHY

Books

Parson, E. A. Protecting the Ozone Layer: Science and Strategy. New York: Oxford University Press, 2003.

Web Sites

“Emissions of Greenhouse Gases in the United States 2005.” U.S. Energy Information Administration. <http://www.eia.doe.gov/oiaf/1605/ggrpt/index.html> (accessed November 12, 2007).

“High Global Warming Potential (GWP) Gases.” U.S. Environmental Protection Agency (EPA), October 20, 2006. <http://www.epa.gov/highgwp/sources.html> (accessed November 3, 2007).

Tony Hawas

Climate Change: In Context