Sources and Emissions

Where do high GWP gas emissions come from?

High GWP gases are emitted from a variety of industrial processes including aluminum production, semiconductor manufacturing, electric power transmission, magnesium production and processing, and the production of HCFC-22. In addition, some high GWP gases are being used to replace ozone-depleting substitutes (i.e., chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and halons) allowing the rapid phase out of these gases.

Table 1 shows the level of emissions from individual sources for the years 1990 and 1997 to 2003.

Table 1 U.S. High GWP Gas Emissions by Source (TgCO₂ Equivalents)

Source: US Emissions Inventory 2005: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003

The principle sources of high GWP gases are described below. For each source, a link is provided to the report entitled "US Emissions Inventory 2006: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2004," prepared by EPA, which provides detailed information on the characterization and quantity of national emissions from each source. This report, hereafter referred to as "the U.S. inventory report", provides the latest descriptions and emissions associated with each source category and is part of the United States’ official submittal to the United Nations Framework Convention on Climate Change (UNFCCC). The U.S. inventory report also describes the procedures used to quantify national emissions, as well as a description of trends in emissions since 1990.

Also, for those sources where EPA has established voluntary programs for reducing high GWP gas emissions, a link to those program sites is provided. For information on international sources and emission of high GWP gases, visit the visit the Non-CO2 Gases Economic Analysis & Inventory Web site.

Substitution of ozone-depleting Substances. ozone-depleting substances (ODSs) including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and halons have been or are in the process of being phased out under the Montreal Protocol and Clean Air Act Amendments of 1990. Under Section 612 of the Clean Air Act, the U.S. EPA established the Significant New Alternatives Policy (SNAP) program to specify acceptable uses for alternatives to ODSs based on their health and environmental risks. The EPA has reviewed hundreds of new alternatives for dozens of consumer, industrial and military applications, and has identified acceptable uses and conditions for a variety of HFCs and in some limited cases, PFCs. The use of HFCs and a broad range of other alternatives has allowed the rapid phaseout of ODSs in the U.S. and other countries. HFCs have generally been selected for applications where they provide superior technical (energy efficiency and reliability) or safety (low toxicity and flammability) performance. HFCs are expected to replace a significant portion of past and current demand for CFCs and HCFCs in insulating foams, refrigeration and air-conditioning, fire suppression, solvent cleaning, and propellants used in aerosols and metered dose inhalers.

The U.S. inventory report provides detailed descriptions on HFC and PFC emissions from the substitution of ozone-depleting substances and how they are estimated (see the Chapter entitled “Industrial Processes”).

Aluminum Production. During primary aluminum production, PFCs (CF₄ and C₂F₆) are emitted as byproducts of the smelting process. The U.S. inventory report provides detailed descriptions on PFC emissions from the primary aluminum production industry and how they are estimated (see the Chapter entitled “Industrial Processes”).

In 1995, EPA, eight of the nation's nine primary aluminum companies and the Aluminum Association created the Voluntary Aluminum Industrial Partnership (VAIP). The main goal of this partnership is to reduce PFC emissions while increasing the efficiency of aluminum production.

Semiconductor Manufacturing. The semiconductor industry uses several high GWP gases in plasma etching and in cleaning chemical vapor deposition (CVD) tool chambers. These processes use plasma-generated fluorine atoms that react at the semiconductor and equipment surface to selectively create circuitry patterns and remove deposited materials. The U.S inventory report provides detailed descriptions on HFCs, PFCs, and SF₆ emissions from semiconductor manufacturing and how they are estimated (see the Chapter entitled “Industrial Processes”).

As part of EPA's PFC Reduction/Climate Partnership for the Semiconductor Industry, the Semiconductor Industry Association (SIA), on behalf of the 22 U.S. semiconductor manufacturers, and the National Security Agency (NSA), collaborate with EPA to identify and implement technologies and process changes that cost-effectively protect the climate. The goal of EPA’s partnership with SIA is to support the World Semiconductor Council’s efforts to reduce the global industry’s PFC emissions 10 percent below the 1995 baseline by 2010.

Electrical Transmission and Distribution. The primary user of SF₆ is the electric power industry. Because of its inertness and dielectric (non-conductive) properties, SF₆ is the industry's preferred gas for electrical insulation, current interruption, and arc quenching in the transmission and distribution of electricity. SF₆ is used extensively in circuit breakers, gas-insulated substations, and switchgear. The U.S. inventory report provides detailed descriptions on SF₆ emissions from electrical transmission and distribution and how they are estimated (see the Chapter entitled “Industrial Processes").

EPA has also established a voluntary program, called the SF₆ Emissions Reduction Partnership for Electric Power Systems, which works with the electric power industry to reduce SF₆ emissions.

Magnesium Production and Processing. The magnesium metal production and casting industry uses SF₆ as a protective cover gas during the processes. SF₆ improves safety and metal quality by preventing the oxidation and potential burning of molten magnesium in the presence of air. SF₆ has been used in this application around the world for more than twenty years. It has largely replaced salt fluxes and sulfur dioxide (SO₂), which are more toxic and corrosive than SF₆. The U.S. inventory report provides detailed descriptions on SF₆ emissions from magnesium production and processing and how they are estimated (see the Chapter entitled “Industrial Processes”).

EPA and the magnesium industry are working together through the voluntary SF₆ Emission Reduction Partnership for the Magnesium Industry, to achieve the industry's climate protection goal of eliminating SF₆ use by 2010.

HFC-23 from HCFC-22 Production. The only significant emissions of HFCs before 1990 resulted from generation of HFC-23 as a byproduct of the production of HCFC-22. HCFC-22 is currently used in refrigeration and air-conditioning systems and as a chemical feedstock for manufacturing synthetic polymers. The U.S. inventory report provides detailed descriptions on HFC-23 emissions from HCFC-22 production and how they are estimated (see the Chapter entitled “Industrial Processes”).

EPA Home | Privacy and Security Notice | Contact Us