Overview of Greenhouse Gases
Emissions of Fluorinated Gases
|Chemical Formula||HFCs, PFCs, SF6|
|Lifetime in Atmosphere||HFCs: 1-270 years
PFCs: 800-50,000 years
SF6: 3,200 years
|Global Warming Potential (100-year)||HFCs: 140-11,700
U.S. Fluorinated Gas Emissions, By Source
Unlike many other greenhouse gases, fluorinated gases have no natural sources and only come from human-related activities. They are emitted through a variety of industrial processes such as aluminum and semiconductor manufacturing. Many fluorinated gases have very high global warming potentials (GWPs) relative to other greenhouse gases, so small atmospheric concentrations can have large effects on global temperatures. They can also have long atmospheric lifetimes--in some cases, lasting thousands of years. Like other long-lived greenhouse gases, fluorinated gases are well-mixed in the atmosphere, spreading around the world after they're emitted. Fluorinated gases are removed from the atmosphere only when they are destroyed by sunlight in the far upper atmosphere. In general, fluorinated gases are the most potent and longest lasting type of greenhouse gases emitted by human activities.
There are three main categories of fluorinated gases--hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). The largest sources of fluorinated gas emissions are described below.
- Substitution for Ozone-Depleting Substances. Hydrofluorocarbons are used as refrigerants, aerosol propellants, solvents, and fire retardants. The major emissions source of these compounds is their use as refrigerants--for example, in air conditioning systems in both vehicles and buildings. These chemicals were developed as a replacement for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) because they do not deplete the stratospheric ozone layer. Chlorofluorocarbons and HCFCs are being phased out under an international agreement, called the Montreal Protocol. Unfortunately, HFCs are potent greenhouse gases with long atmospheric lifetimes and high GWPs, and they are released into the atmosphere through leaks, servicing, and disposal of equipment in which they are used.
- Industry. Perfluorocarbons are compounds produced as a by-product of various industrial processes associated with aluminum production and the manufacturing of semiconductors. Like HFCs, PFCs generally have long atmospheric lifetimes and high GWPs. Sulfur hexafluoride is used in magnesium processing and semiconductor manufacturing, as well as a tracer gas for leak detection. HFC-23 is produced as a by-product of HCFC-22 production.
- Transmission and Distribution of Electricity. Sulfur hexafluoride is used in electrical transmission equipment, including circuit breakers. The GWP of SF6 is 23,900, making it the most potent greenhouse gases that the Intergovernmental Panel on Climate Change has evaluated.
To find out more about the role of fluorinated gases in warming the atmosphere, and their sources, visit the Causes of Climate Change page and the Greenhouse Gas Indicators page in the Science section.
Emissions and Trends
Overall, fluorinated gas emissions in the United States have increased by about 61% between 1990 and 2011. This increase has been driven by a 249% increase in emissions of hydrofluorocarbons (HFCs) since 1990 as they have been widely used as a substitute for ozone-depleting substances. Emissions of perfluorocarbons (PFCs) and sulfur hexafluoride (SF6) have actually declined during this time due to emission reduction efforts in the aluminum production industry (PFCs) and the electricity transmission and distribution industry (SF6).
Going forward, HFC emissions are projected to grow by nearly 140% between 2005 and 2020 as demands for refrigeration continue to grow and as more ozone-depleting substances are replaced. During this same period, emissions of SF6 are expected to decline by over 25%, while emissions of PFCs are projected to remain flat. Since the emissions from HFCs are far greater than the emissions of the other gases on a carbon dioxide-equivalence basis, substantial growth in emissions of F-gases is expected to continue. 
U.S. Fluorinated Gas Emissions, 1990-2011
Reducing Fluorinated Gas Emissions
Because most fluorinated gases have a very long atmospheric lifetime, it will take many years to see a noticeable decline in current concentrations. However, there are a number of ways to reduce emissions of fluorinated gases, described below.
|Emissions Source||Examples of How Emissions Can be Reduced|
Substitution of Ozone-Depleting Substances in Homes and Businesses
Refrigerants used by businesses and residences emit fluorinated gases. Emissions can be reduced by use of substitutes with lower global warming potentials and other technological improvements. Visit EPA's Ozone Layer Protection site to learn more about reduction opportunities in this sector.
Industrial users of fluorinated gases can reduce emissions by adopting fluorinated gas recycling and destruction processes, optimizing production to minimize emissions, and replacing these gases with alternatives. The following are EPA programs working to reduce these gases in the Industry sector:
Electricity Transmission and Distribution
Sulfur hexafluoride is an extremely potent greenhouse gas that is used for several purposes when transmitting electricity through the power grid. EPA is working with industry to reduce emissions through the SF6 Emission Reduction Partnership for Electric Power Systems which promotes leak detection and repair, use of recycling equipment, and employee training.
Hydrofluorocarbons (HFCs) are released through the leakage of refrigerants used in vehicle air-conditioning systems. Leakage can be reduced through better system components, and through the use of alternative refrigerants with lower global warming potentials than those presently used. One important way the EPA is working to reduce HFC emissions is through its light-duty and heavy-duty vehicle standards.
1. U.S. Department of State (2007). Projected Greenhouse Gas Emissions In: Fourth Climate Action Report to the UN Framework Convention on Climate Change . U.S. Department of State, Washington, DC, USA.
Global Warming Potential Describes Impact of Each Gas
Certain greenhouse gases (GHGs) are more effective at warming Earth ("thickening the blanket") than others.The two most important characteristics of a GHG in terms of climate impact are how well the gas absorbs energy (preventing it from immediately escaping to space), and how long the gas stays in the atmosphere.
The Global Warming Potential (GWP) for a gas is a measure of the total energy that a gas absorbs over a particular period of time (usually 100 years), compared to carbon dioxide. The larger the GWP, the more warming the gas causes. For example, methane's 100-year GWP is 21, which means that methane will cause 21 times as much warming as an equivalent mass of carbon dioxide over a 100-year time period.
- Carbon dioxide (CO2) has a GWP of 1 and serves as a baseline for other GWP values. CO2 remains in the atmosphere for a very long time - changes in atmospheric CO2 concentrations persist for thousands of years.
- Methane (CH4) has a GWP more than 20 times higher than CO2 for a 100-year time scale. CH4 emitted today lasts for only about a decade in the atmosphere, on average. However, on a pound-for-pound basis, CH4 absorbs more energy than CO2, making its GWP higher.
- Nitrous Oxide (N2O) has a GWP 300 times that of CO2 for a 100-year timescale. N2O emitted today remains in the atmosphere for more than 100 years, on average.
Chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) are sometimes called high-GWP gases because, for a given amount of mass, they trap substantially more heat than CO2.
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