The rotten-egg smell of a gas leak is added on purpose
Methane, the main ingredient of natural gas, has no colour and no smell at all. The stink you notice near a leaking stove comes from an odorant such as methanethiol, deliberately mixed in because it resembles hydrogen sulfide. Without it, a room could fill with an explosive gas and nobody would notice until too late.
Natural gas is typically about 95 percent methane, with small amounts of heavier hydrocarbons and traces of carbon dioxide, nitrogen, hydrogen sulfide and helium. It forms when layers of organic matter, mostly marine microorganisms, are cooked without oxygen under intense heat and pressure for millions of years, locking ancient sunlight captured by photosynthesis into chemical bonds. Before it is sold, processors strip out water and sulfur compounds and recover ethane, propane and butane for other uses.
People met it long before they piped it. Flames burning from the ground at Mount Chimaera in ancient Greece fed the legend of the fire-breathing Chimera. By about 400 BC, Chinese salt makers in Sichuan were channelling seeping gas through bamboo pipes to boil brine. In America, French missionaries in the seventeenth century watched Native Americans set fire to seeps around Lake Erie, and William Hart dug the country's first commercial gas well at Fredonia, New York, in 1821.
The word natural was coined in the early 1800s to set it apart from coal gas, which was manufactured by heating coal and dominated lighting in the industrial era. For a long time gas that bubbled out of oil wells, like fizz from an opened soft drink, was treated as a nuisance and vented or burned off. Only long-distance pipelines from the 1920s, and later liquefied shipping, let it travel. Since 2000, hydraulic fracturing of shale has made the United States and Canada major producers, and by 2014 the United States led the world.
Burning gas releases less carbon dioxide and almost no soot compared with coal or oil. Leaks and deliberate venting complicate that picture, since methane ranks second only to carbon dioxide as a greenhouse gas, and some critics prefer the names fossil gas or methane gas for that reason. The largest known field, South Pars and North Dome, lies offshore and is shared by Iran and Qatar.
Source: Natural gas
