Methane, colourless, odourless gas that occurs abundantly in nature and as a product of certain human activities. Methane is the simplest member of the paraffin series of hydrocarbons and is among the most potent of the greenhouse gases. Its chemical formula is CH4.
Chemical properties of methane
Methane is lighter than air, having a specific gravity of 0.554. It is only slightly soluble in water. It burns readily in air, forming carbon dioxide and water vapour; the flame is pale, slightly luminous, and very hot. The boiling point of methane is −162 °C (−259.6 °F) and the melting point is −182.5 °C (−296.5 °F). Methane in general is very stable, but mixtures of methane and air, with the methane content between 5 and 14 percent by volume, are explosive. Explosions of such mixtures have been frequent in coal mines and collieries and have been the cause of many mine disasters.
Sources of methane
In nature, methane is produced by the anaerobic bacterial decomposition of vegetable matter under water (where it is sometimes called marsh gas or swamp gas). Wetlands are the major natural source of methane produced in this way. Other important natural sources of methane include termites (as a result of digestive processes), volcanoes, vents in the ocean floor, and methane hydrate deposits that occur along continental margins and beneath Antarctic ice and Arctic permafrost. Methane also is the chief constituent of natural gas, which contains from 50 to 90 percent methane (depending on the source), and occurs as a component of firedamp (flammable gas) along coal seams. The production and combustion of natural gas and coal are the major anthropogenic (human-associated) sources of methane. Activities such as the extraction and processing of natural gas and the destructive distillation of bituminous coal in the manufacture of coal gas and coke-oven gas result in the release of significant amounts of methane into the atmosphere. Other human activities that are associated with methane production include biomass burning, livestock farming, and waste management (where bacteria produce methane as they decompose sludge in waste-treatment facilities and decaying matter in landfills).
Uses of methane
Methane is an important source of hydrogen and some organic chemicals. Methane reacts with steam at high temperatures to yield carbon monoxide and hydrogen; the latter is used in the manufacture of ammonia for fertilizers and explosives. Other valuable chemicals derived from methane include methanol, chloroform, carbon tetrachloride, and nitromethane. The incomplete combustion of methane yields carbon black, which is widely used as a reinforcing agent in rubber used for automobile tires.
Climate Impacts - Methane is generally considered second to carbon dioxide in its importance to climate change. The presence of methane in the atmosphere can also affect the abundance of other greenhouse gases, such as tropospheric ozone, water vapor and carbon dioxide.
Health Impacts - Methane is a key precursor gas of the harmful air pollutant, tropospheric ozone. Globally, increased methane emissions are responsible for half of the observed rise in tropospheric ozone levels. While methane does not cause direct harm to human health or crop production, ozone is responsible for about 1 million premature respiratory deaths globally. Methane is responsible for about half of these deaths.
Importance of Methane
Methane (CH4) is a hydrocarbon that is a primary component of natural gas. Methane is also a greenhouse gas (GHG), so its presence in the atmosphere affects the earth’s temperature and climate system. Methane is emitted from a variety of anthropogenic (human-influenced) and natural sources. Anthropogenic emission sources include landfills, oil and natural gas systems, agricultural activities, coal mining, stationary and mobile combustion, wastewater treatment, and certain industrial processes. Methane is the second most abundant anthropogenic GHG after carbon dioxide (CO2), accounting for about 20 percent of global emissions. Methane is more than 25 times as potent as carbon dioxide at trapping heat in the atmosphere. Over the last two centuries, methane concentrations in the atmosphere have more than doubled, largely due to human-related activities. Because methane is both a powerful greenhouse gas and short-lived compared to carbon dioxide, achieving significant reductions would have a rapid and significant effect on atmospheric warming potential.