Natural gas

Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%),^[1] small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium.^[2] Methane is a colorless and odorless gas, and, after carbon dioxide, is the second-greatest greenhouse gas that contributes to global climate change.^[3][4] Because natural gas is odorless, a commercial odorizer, such as Methanethiol (mercaptan brand), that smells of hydrogen sulfide (rotten eggs) is added to the gas for the ready detection of gas leaks.^[5]

Natural gas is a fossil fuel that is formed when layers of organic matter (primarily marine microorganisms)^[6] are thermally decomposed under oxygen-free conditions, subjected to intense heat and pressure underground over millions of years.^[7] The energy that the decayed organisms originally obtained from the sun via photosynthesis is stored as chemical energy within the molecules of methane and other hydrocarbons.^[8]

Natural gas can be burned for heating, cooking,^[9] and electricity generation. Consisting mainly of methane, natural gas is rarely used as a chemical feedstock.

The extraction and consumption of natural gas is a major industry. When burned for heat or electricity, natural gas emits fewer toxic air pollutants, less carbon dioxide, and almost no particulate matter compared to other fossil fuels.^[10] However, gas venting and unintended fugitive emissions throughout the supply chain can result in natural gas having a similar carbon footprint to other fossil fuels overall.^[11]

Natural gas can be found in underground geological formations, often alongside other fossil fuels like coal and oil (petroleum). Most natural gas has been created through either biogenic or thermogenic processes. Thermogenic gas takes a much longer period of time to form and is created when organic matter is heated and compressed deep underground.^[12][7] Methanogenic organisms produce methane from a variety of sources, principally carbon dioxide.

During petroleum production, natural gas is sometimes flared rather than being collected and used. Before natural gas can be burned as a fuel or used in manufacturing processes, it almost always has to be processed to remove impurities such as water. The byproducts of this processing include ethane, propane, butanes, pentanes, and higher molecular weight hydrocarbons. Hydrogen sulfide (which may be converted into pure sulfur), carbon dioxide, water vapor, and sometimes helium and nitrogen must also be removed.

Natural gas is sometimes informally referred to simply as "gas", especially when it is being compared to other energy sources, such as oil, coal or renewables. However, it is not to be confused with gasoline, which is also shortened in colloquial usage to "gas", especially in North America.^[13]

Natural gas is measured in standard cubic meters or standard cubic feet. The density compared to air ranges from 0.58 (16.8 g/mole, 0.71 kg per standard cubic meter) to as high as 0.79 (22.9 g/mole, 0.97 kg per scm), but generally less than 0.64 (18.5 g/mole, 0.78 kg per scm).^[14] For comparison, pure methane (16.0425 g/mole) has a density 0.5539 times that of air (0.678 kg per standard cubic meter).