Methane
What type of substance is it?
Methane is both a common naturally occuring chemical and is manufactured by man. Methane is the second most important "greenhouse gas" (after carbon dioxide) resulting from human activities. Releasing it to the atmosphere is thought to contribute to global warming.
How is it released?
Methane is a trace constituent of the atmosphere. Man made sources include natural gas extraction and transportation (methane is the main component of natural gas) waste disposal, agriculture and coal mining. Methane is also released in significant amounts by marshland, rice paddies and by ruminant animals (e.g. cattle, sheep) and termites.
Detailed information
Scientific name: Methane, CH4
Other names: Natural gas; methyl hydride; marsh gas; biogas; fire damp; R 50 (refrigerant)
CAS Number: 74-82-8
Over the last two centuries, methane concentrations in the atmosphere have more than doubled, largely due to human activities. However, recent concerns over the global warming impacts of methane (it has a much greater warming effect on the climate than carbon dioxide) have resulted in measures to reduce the human induced emissions.
As the major constituent of natural gas, methane is burned to directly heat homes and other commercial buildings. It is also used as a fuel in power stations to produce electricity. Methane is used widely in the chemicals industry in the production of more complex chemical compounds.
Methane is a colourless gas, odourless at low concentrations, but with a sweetish chloroform-like odour at high concentration. It is highly combustible, and mixtures of about 5 to 15 percent in air are explosive. Upon release into the atmosphere methane is destroyed by reactions with other chemicals in the atmosphere, giving it a lifetime of about 10 years.
Where is it released?
Methane occurs naturally in the environment. One of the major sources is from the decomposition of plant and animal matter by methane producing bacteria. These occur in air-less environments such as marshes and the guts of some animals and landfills. Methane is also trapped in pockets with the earth's crust, and can be released during the mining of fossil fuels. In the UK the major sources of methane from human activity are waste disposal, agriculture, coal mining and leakage from the gas distribution system. In 1996 Landfill sites accounted for an estimated 46% (1996) of the UK's methane emissions. The second largest source of emissions was from the agricultural sector, principally from the grazing of livestock and animal wastes. Methane emission form coal mining have reduced significantly during the past 20 years, however, it still provides a significant contribution. Leakage in the pipelines and distribution systems of the gas network allow methane releases in to the environment. Offshore oil and gasworks contribute 2% of emissions, methane is also released by sewage disposal. On a global scale, the human activities that result in the most methane emission, in descending order of importance are; livestock farming, production of fossil fuels, wet rice cultivation, biomass burning, landfill and domestic sewage.
Local environmental effects
Methane gas build-up from landfill sites is a potential explosion hazard. In the past this has resulted in a few temporary evacuations of residents in housing estates built on top of old landfill sites that have not sufficiently vented the methane. As a volatile organic compound (VOC) it has been determined to have negligable photochemical reactivity and is unlikely to contribute significantly to the formation of harmful ground level ozone or (photochemical) smogs.
Global environmental effects
The main impact of methane on the environment is as a greenhouse gas, leading to global warming. Over the last two centuries, methane concentrations in the atmosphere have more than doubled, largely due to human-related activities. Methane is the second most important greenhouse gas, after carbon dioxide. Although less emissions of methane are emitted into the environment the Global Warming potential of Methane is 21 times that of CO2, over 100 years. The concept of Global Warming Potential has been developed to compare the ability of each greenhouse gas to trap heat in the atmosphere relative to another gas. CO2 has a GWP of 1 (over 100 years).
Possible health concerns
Excessive exposure to methane may affect the brain. The Environment Agency aims to ensure that environmental exposures are too low to harm human health.
Legislation
Why was this substance selected for the Pollution Inventory?
Included in : European Pollutant Emission Register (EPER) reporting requirements; United Nations Framework Convention on Climate Change (UNFCCC) Kyoto Protocol reporting requirements; Environment Agency categorisation as a hazardous Volatile Organic Compound (VOC).
Standard risk phrases for the pure substance
The standard risk phrases provided here are generally those used by suppliers of chemicals to describe substances - for example on packaging materials. The most important source of these phrases are the CHIP Regulations - Chemicals (Hazard Information and Packaging for Supply) - provided by the Health and Safety Executive. Some substances do not have CHIP risk phrases and in these circumstances we have used other risk phrases, the sources of which are indicated.
CHIP Phrase(s) : F+: Extremely Flammable; R12: Extremely Flammable
Controlling legislation and international agreements
The UK government is committed to reduce emissions of the six main greenhouse gases, including methane, under the United Nations Framework Convention on Climate Change (Kyoto Protocol). The target for the UK is to achieve a reduction of the global warming potential of the six greenhouse gases of 12.5% by 2008-2012 (based on 1990 emissions estimates). As a VOC the main international legislation are the UN/ECE Convention on Long-Range Transboundary Air Pollution and Basel Conventions. The UK is also committed to reduce VOC emissions under its Air Quality Strategy.
These factsheets have been compiled to provide users with information on the Pollution Inventory substances and represent our best efforts to summarise a large number of disparate and sometimes conflicting data sources. We emphasise that this information describes potential hazards rather than actual effects and that the Environment Agency seeks to regulate releases to minimise emissions and hence any risk of detrimental effects occurring.