Methane | Engineering | Fandom powered by Wikia Edit At room temperature and pressure, methane is a colourless, odourless gas. It has boiling point of −162° C at 1 atmosphere pressure and is highly flammable . Pure methane is odorless , but when used commercially is usually mixed with small quantities of odorants, strongly-smelling sulfur compounds such as ethyl mercaptan to enable the detection of leaks. Burning one molecule of methane in the presence of oxygen releases one molecule of CO2 ( carbon dioxide ) and two molecules of H2O ( water ): CH4 + 2O2 → CO2 + 2H2O Methane is a greenhouse gas . Methane has a wide range of thermodynamic stability. It has a mass of 16.05. Potential health effects Edit Methane is not toxic by any route. The immediate health hazard is that it may cause thermal burns . It is flammable and may form mixtures with air that are flammable or explosive . Methane is violently reactive with oxidizers , halogens , and some halogen compounds. Methane is an asphyxiant and may displace oxygen in a workplace atmosphere.

Asphyxia may result if the oxygen concentration is reduced to below 18% by displacement. The concentrations at which flammable or explosive mixtures form are much lower than the concentration at which asphyxiation risk is significant. Reactions of methane The reactions with methane are: combustion, hydrogen activation, and halogen reaction. Combustion Methane is a significant fuel . In the combustion of methane several steps are involved: Methane forms a methyl radical ( ), which reacts with oxygen forming formaldehyde ( or ), which then forms carbon monoxide ( ). The process is called oxidative pyrolysis : Following oxidative pyrolysis, the oxidizes, forming , replenishing the active species, and releasing heat . This occurs very quickly, usually in less than a millisecond . Finally, the oxidizes , forming and releasing more heat. This process is generally slower than the other chemical steps, and typically requires a few to several milliseconds to occur. Hydrogen activation Edit The strength of the carbon - hydrogen covalent bond[ [2] ] in methane is among the strongest in all hydrocarbons, and thus its use as a chemical feedstock is limited.

Despite the high activation barrier for breaking the C-H bond, CH4 is still the principal starting material for manufacture of hydrogen. The search for catalysts which can facilitate C-H bond activation in methane and other low alkanes is an area of research with considerable industrial significance. Reactions with halogens Methane undergoes reactions with all the halogens give correct conditions. The reactions occur as follows: Where is either Fluorine (F), Chlorine (Cl), Bromine (Br) or sometimes Iodine (I). This mechanism for this process is called free radical substitution[ [3] ] and it occurs as follows: Initiation: Edit Methane is a principal component of natural gas . Large amounts of methane are emitted to atmosphere through Mud volcanoes which are connected with deep geological faults. Natural gas fields Edit The major source of methane is extraction from geological deposits known as natural gas fields . It is associated with other hydrocarbon fuels and sometimes accompanied by helium and nitrogen . The gas at shallow levels (low pressure) is formed by anaerobic decay of organic matter deep under the Earth's surface. In general, sediments buried deeper and at higher temperatures than those which give oil generate natural gas.

Alternative sources Edit Apart from gas fields an alternative method of obtaining methane is via biogas generated by the fermentation of organic matter including manure , wastewater sludge, municipal solid waste, or any other biodegradable feedstock, under anaerobic conditions. Industrially, methane can be created from common atmospheric gases and hydrogen (produced, perhaps, by electrolysis ) through chemical reactions such as the Sabatier process[ [4] ], Fischer-Tropsch process[ [5] ]. Coal bed methane extraction is a method for extracting methane from a coal deposit. Methane in the earth's atmosphere is an important greenhouse gas with a Global warming potential of 23 over a 100 year period. Emissions of methane Houweling et al. (1999) give the following values for methane emissions [6] : Origin Edit For more on the use of methane as a fuel, see: natural gas Methane is an important fuel for electrical generation . Compared to other Hydrocarbon fuels , burning methane produces less carbon dioxide for each unit of heat released.

Also, Methane's heat of combustion is about 902 kJ/mol, which is lower than any other hydrocarbon, but if a ratio is made with the atomic weight (16 g/mol) divided by the heat of combustion (902 kJ/mol) it is found that methane, being the simplest hydrocarbon, actually produces the most heat per gram than other complex hydrocarbons. In many cities, methane is piped into homes for domestic heating and cooking purposes. In this context it is usually known as natural gas. Industrial uses Edit Methane is used in industrial chemical processes and may be transported in liquid or refrigerated liquid form. While leaks from a liquid container are initially heavier than air, the gas is lighter than air. Gas pipelines distribute large amounts of natural gas , of which methane is a significant component. In the chemical industry, methane is the feedstock of choice for the production of hydrogen , methanol , acetic acid , and acetic anhydride . When used to produce any of these chemicals, methane is first converted to synthesis gas , a mixture of carbon monoxide and hydrogen , by steam reforming .

In this process, methane and steam react on a nickel catalyst at high temperatures (700–1100 °C). The ratio of carbon monoxide to hydrogen in synthesis gas can then be adjusted via the water gas shift reaction to the appropriate value for the intended purpose. Less significant methane-derived chemicals include acetylene , prepared by passing methane through an electric arc , and the chloromethanes ( chloromethane , dichloromethane , chloroform , and carbon tetrachloride ), produced by reacting methane with chlorine gas. However, the use of these chemicals is declining, acetylene as it is replaced by less costly substitutes, and the chloromethanes due to health and environmental concerns. See also methane | chemical compound | Britannica.com chemical compound biogas 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. Encyclopædia Britannica, Inc.

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. The tetrahedral structure of methane (CH4) is explained in the VSEPR … Encyclopædia Britannica, Inc. 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. Learn about the emission of methane, a greenhouse gas, by trees in wetland ecosystems. © Open University (A Britannica Publishing Partner) The tetrahedral geometry of methane: (A) stick-and-ball model and (B) showing bond angles and … Encyclopædia Britannica, Inc. wood 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 . Role as a greenhouse gas Methane that is produced and released into the atmosphere is taken up by methane sinks, which include soil and the process of methane oxidation in the troposphere (the lowest atmospheric region). Most methane produced naturally is offset by its uptake into natural sinks. Anthropogenic methane production, however, can cause methane concentrations to increase more quickly than they are offset by sinks.

Increased concentrations of methane in the atmosphere contribute to the greenhouse effect , whereby greenhouse gases (particularly carbon dioxide , methane, and water vapour) absorb infrared radiation (net heat energy) and reradiate it back to Earth ’s surface, potentially trapping heat and producing substantial changes in climate . Increased atmospheric methane also adds to the greenhouse effect indirectly. For example, in methane oxidation hydroxyl radicals (OH−) remove methane by reacting with it to form carbon dioxide and water vapour, and as concentrations of atmospheric methane increase, concentrations of hydroxyl radicals decrease, effectively prolonging the atmospheric lifetime of methane. Learn More in these related articles: in climate (meteorology) Chemical formula for methane Methane Chemical formula for methane Methane is a colorless highly flammable gas that is less dense than air. The methane molecule consists of four hydrogen atoms covalently one carbon atom. The chemical formula for methane is CH4 which is the simplest hydrocarbon of the alkane series. The molar mass of methane is 16.043 g/mol Methane is a major component of natural gas and is also produced from by anaerobic bacteria in septic tanks and in the digestive systems of animals.

Methane readily undergoes combustion producing carbon dioxide and water. Methane + oxygen ==> carbon dioxide + water + energy CH4 + 2O2 ==> CO2 + 2H2O + energy Greenhouse Gases | Monitoring References | National Centers for Environmental Information (NCEI) Introduction What are greenhouse gases? Many chemical compounds present in Earth's atmosphere behave as 'greenhouse gases'. These are gases which allow direct sunlight (relative shortwave energy) to reach the Earth's surface unimpeded. As the shortwave energy (that in the visible and ultraviolet portion of the spectra) heats the surface, longer-wave (infrared) energy (heat) is reradiated to the atmosphere. Greenhouse gases absorb this energy, thereby allowing less heat to escape back to space, and 'trapping' it in the lower atmosphere. Many greenhouse gases occur naturally in the atmosphere, such as carbon dioxide, methane, water vapor, and nitrous oxide, while others are synthetic.

Those that are man-made include the chlorofluorocarbons (CFCs) , hydrofluorocarbons (HFCs) and Perfluorocarbons (PFCs), as well as sulfur hexafluoride (SF6). Atmospheric concentrations of both the natural and man-made gases have been rising over the last few centuries due to the industrial revolution. As the global population has increased and our reliance on fossil fuels (such as coal, oil and natural gas) has been firmly solidified, so emissions of these gases have risen. While gases such as carbon dioxide occur naturally in the atmosphere, through our interference with the carbon cycle (through burning forest lands, or mining and burning coal), we artificially move carbon from solid storage to its gaseous state, thereby increasing atmospheric concentrations. Water Vapor Water Vapor is the most abundant greenhouse gas in the atmosphere, which is why it is addressed here first. However, changes in its concentration is also considered to be a result of climate feedbacks related to the warming of the atmosphere rather than a direct result of industrialization. The feedback loop in which water is involved is critically important to projecting future climate change, but as yet is still fairly poorly measured and understood.

As the temperature of the atmosphere rises, more water is evaporated from ground storage (rivers, oceans, reservoirs, soil). Because the air is warmer, the absolute humidity can be higher (in essence, the air is able to 'hold' more water when it's warmer), leading to more water vapor in the atmosphere. As a greenhouse gas, the higher concentration of water vapor is then able to absorb more thermal IR energy radiated from the Earth, thus further warming the atmosphere. The warmer atmosphere can then hold more water vapor and so on and so on. This is referred to as a 'positive feedback loop'. However, huge scientific uncertainty exists in defining the extent and importance of this feedback loop. As water vapor increases in the atmosphere, more of it will eventually also condense into clouds, which are more able to reflect incoming solar radiation (thus allowing less energy to reach the Earth's surface and heat it up). The future monitoring of atmospheric processes involving water vapor will be critical to fully understand the feedbacks in the climate system leading to global climate change. As yet, though the basics of the hydrological cycle are fairly well understood, we have very little comprehension of the complexity of the feedback loops.

Also, while we have good atmospheric measurements of other key greenhouse gases such as carbon dioxide and methane, we have poor measurements of global water vapor, so it is not certain by how much atmospheric concentrations have risen in recent decades or centuries, though satellite measurements, combined with balloon data and some in-situ ground measurements indicate generally positive trends in global water vapor. Carbon Dioxide The natural production and absorption of carbon dioxide (CO2) is achieved through the terrestrial biosphere and the ocean. However, humankind has altered the natural carbon cycle by burning coal, oil, natural gas and wood and since the industrial revolution began in the mid 1700s, each of these activities has increased in scale and distribution. Carbon dioxide was the first greenhouse gas demonstrated to be increasing in atmospheric concentration with the first conclusive measurements being made in the last half of the 20th century. Prior to the industrial revolution, concentrations were fairly stable at 280ppm. Today, they are around 370ppm, an increase of well over 30 percent. The atmospheric concentration has a marked seasonal oscillation that is mostly due to the greater extent of landmass in the northern hemisphere and its vegetation.

A greater drawdown of CO2 occurs in the northern hemisphere spring and summer as plants convert CO2 to plant material through photosynthesis. It is then released again in the fall and winter as the plants decompose. Methane Methane (CH4) is an extremely effective absorber of radiation, though its atmospheric concentration is less than CO2 and its lifetime in the atmosphere is brief (10-12 years), compared to some other greenhouse gases (such as CO2, N2O, CFCs ). Methane has both natural and anthropogenic sources. It is released as part of the biological processes in low oxygen environments, such as in swamplands or in rice production (at the roots of the plants). Over the last 50 years, human activities such as growing rice, raising cattle, using natural gas and mining coal have added to the atmospheric concentration of methane. Direct atmospheric measurement of atmospheric methane has been possible since the late 1970s and its concentration rose from 1.52 ppmv in 1978 by around 1 percent per year to 1990, since when there has been little sustained increase.

The current atmospheric concentration is approximately 1.77 ppmv, and there is no scientific consensus on why methane has not risen much since around 1990. Tropospheric Ozone Ultraviolet radiation and oxygen interact to form ozone in the stratosphere. Existing in a broad band, commonly called the 'ozone layer', a small fraction of this ozone naturally descends to the surface of the Earth. However, during the 20th century, this tropospheric ozone has been supplemented by ozone created by human processes. The exhaust emissions from automobiles and pollution from factories (as well as burning vegetation) leads to greater concentrations of carbon and nitrogen molecules in the lower atmosphere which, when it they are acted on by sunlight, produce ozone. Consequently, ozone has higher concentrations in and around cities than in sparsely populated areas, though there is some transport of ozone downwind of major urban areas. Ozone is an important contributor to photochemical smog.

Though the lifetime of ozone is short, and is therefore not well-mixed through the atmosphere, there is a general band of higher ozone concentration during northern hemisphere spring and summer between 30°N and 50°N resulting from the higher urbanization and industrial activity in this band. Concentrations of ozone have risen by around 30 percent since the pre-industrial era, and is now considered by the IPCC to be the third most important greenhouse gas after carbon dioxide and methane. An additional complication of ozone is that it also interacts with and is modulated by concentrations of methane. Nitrous Oxide Concentrations of nitrous oxide also began to rise at the beginning of the industrial revolution and is understood to be produced by microbial processes in soil and water, including those reactions which occur in fertilizer containing nitrogen. Increasing use of these fertilizers has been made over the last century. Global concentration for N2O in 1998 was 314 ppb, and in addition to agricultural sources for the gas, some industrial processes (fossil fuel-fired power plants, nylon production, nitric acid production and vehicle emissions) also contribute to its atmospheric load.

Chlorofluorocarbons Chlorofluorocarbons (CFCs) have no natural source, but were entirely synthesized for such diverse uses as refrigerants, aerosol propellants and cleaning solvents. Their creation was in 1928 and since then concentrations of CFCs in the atmosphere have been rising. Due to the discovery that they are able to destroy stratospheric ozone, a global effort to halt their production was undertaken and was extremely successful. So much so that levels of the major CFCs are now remaining level or declining. However, their long atmospheric lifetimes determine that some concentration of the CFCs will remain in the atmosphere for over 100 years. Since they are also greenhouse gas, along with such other long-lived synthesized gases as CF4 (carbon tetrafluoride), SF6 (sulfur hexafluoride), they are of concern. Another set of synthesized compounds called HFCs (hydrofluorocarbons) are also greenhouse gases, though they are less stable in the atmosphere and therefore have a shorter lifetime and less of an impact as a greenhouse gas.

Carbon Monoxide and other reactive gases Carbon monoxide (CO) is not considered a direct greenhouse gas, mostly because it does not absorb terrestrial thermal IR energy strongly enough. However, CO is able to modulate the production of methane and tropospheric ozone. The Northern Hemisphere contains about twice as much CO as the Southern Hemisphere because as much as half of the global burden of CO is derived from human activity, which is predominantly located in the northern hemisphere. Due to the spatial variability of CO, it is difficult to ascertain global concentrations, however, it appears as though they were generally increasing until the late 1980s, and have since begun to decline somewhat. One possible explanation is the reduction in vehicle emissions of CO since greater use of catalytic converters has been made. Volatile Organic Compounds (VOCs) also have a small direct impact as greenhouse gases, as well being involved in chemical processes which modulate ozone production. VOCs include non-methane hydrocarbons (NMHC), and oxygenated NMHCs (eg. alcohols and organic acids), and their largest source is natural emissions from vegetation. However, there are some anthropogenic sources such as vehicle emissions, fuel production and biomass burning.

Though measurement of VOCs is extremely difficult, it is expected that most anthropogenic emissions of these compounds have increased in recent decades. Nature of Petroleum & Natural Gas Nature of Petroleum & Natural Gas text size A A A Nature of Petroleum & Natural Gas Although oil and gas are legally classified as minerals, they differ from most other minerals in several important respects. Most minerals (ie. gold, copper, salt, etc.) are defined by their unique chemical composition. Neither oil nor gas has a unique chemical composition. Both oil and gas are complex solutions consisting primarily of organic compounds. With few exceptions, the structure of an organic compound is based on a carbon atom linked to other atoms (either carbon atoms or atoms of another element) with four covalent bonds (a sharing of electrons between atoms). The simplest such compound found widely in nature is methane (CH4), which consists of a single carbon atom and 4 hydrogen atoms bound together by 4 single covalent bonds. In ethane (C2H6), one of the single carbon-hydrogen covalent bonds in methane is replaced with a carbon-carbon covalent bond.

Methane and ethane are the 1st and 2nd members of the hydrocarbon family known as the paraffins whose chemical formula can be expressed as CnH2n+2, and whose structure is based on a continuous chain of carbon atoms linked with single covalent bonds. This continuous chain structure is usually illustrated as follows: Once the number of carbon atoms in the chain exceeds three, different compounds with the same chemical formula and fundamental binding mechanism but linked through various branching chains become possible. These hydrocarbon compounds, which have different physical properties, are known as "isomers". The number of ways of arranging the branching chains to create isomers increases with the number of carbon atoms in the particular paraffin. Butane (C4H10) has 2 common isomers, pentane (C5H12) has 3, decane (C10H22) has 75. As paraffins containing up to 30 carbon atoms (triacontane (C30H62) have been recognized, the paraffin family itself contains tens of thousands of individual organic compounds each with different physical properties.

The number of carbon atoms in a member of the paraffin series determines whether the hydrocarbon will exist as a gas, a liquid, or a solid, when in isolation. Methane (CH4), in isolation, is a gas under all naturally occurring temperature and pressure conditions. Ethane (C2H6), propane (C3H8), butane (C4H10) and its isomers, in isolation, are gaseous under standard surface conditions (60o Fahrenheit and 14.4 pounds per square inch (psi) pressure) but may exist in either gaseous or liquid phase under the elevated temperature and pressure conditions found in subsurface reservoirs. In isolation, members of the paraffin series with between 5 and 17 carbon atoms in their molecular structures (pentane - C5H12, hexane - C6H14, heptane - C7H16, octane - C8H18, etc. and their isomers) are liquid under standard surface conditions and most temperature and pressure conditions encountered in subsurface reservoirs. Members of the paraffin series with more than 17 carbon atoms are solid under most naturally occurring temperatures and pressures.

In addition to the family of hydrocarbons whose structure is based on continuous chains of carbon atoms linked with single covalent bonds, families based on double covalent bonds, 2 or more double bonds, and triple covalent bonds exist. Furthermore, there is an entire additional group of hydrocarbons in which the carbon atoms are attached to each other in rings rather than chains. Because of their similar molecular structures, most hydrocarbons are soluble in each other. A typical subsurface 'oil' or 'petroleum' contains hundreds of thousands of different hydrocarbon compounds in a complex liquid solution. Subsurface 'gas' is a complex solution of the same hydrocarbons, but in different proportions. The solubility of the various hydrocarbon compounds in each other depends on the temperature and pressure under which they are confined. Subsurface temperatures and pressures typically increase at the rate of approximately 1 degree and 45 psi per hundred feet of depth. Under the relatively high confining temperatures and pressures of the subsurface, all oil contains normally gaseous hydrocarbons such as methane dissolved in liquid solution, and most natural gas contains normally liquid hydrocarbons such as pentanes dissolved in gaseous solution.

As subsurface oil or gas moves from its point of recovery at the bottom of a producing well bore to the surface, it is subject to a rapid decline in confining temperature and pressure. In the case of oil, the reduction in pressure causes normally gaseous hydrocarbons dissolved in the oil to evolve from solution in the well bore and to be produced at surface as gas. A simple analogy would be the bubbles of carbon dioxide observed when one removes the cap from a bottle of soda pop. In the case of gas, the reduction in temperature associated with the production process causes normally liquid hydrocarbons dissolved in the gas at the bottom of the well bore in the subsurface to condense from solution in the well bore and to be produced at surface as liquid 'condensate'. A simple analogy would be the droplets of water that condense on a cold pane of glass when one blows on the glass. Because the gas that evolves from oil as it moves to surface in the production process consists primarily of 'lighter' hydrocarbon compounds such as methane and ethane, the composition of the oil changes significantly between the subsurface and the surface.

These changes have been summarized as follows1: Thirty-four percent of the molecules in the 'typical' subsurface oil described above were methane. Some 'heavy' oils contain less than 5% methane whereas many 'volatile' oils contain more than 50% methane. Because all subsurface oils contain methane and other hydrocarbon compounds which are gaseous under standard surface conditions, all oil wells produce measurable volumes of gas at surface. Because most gas in the subsurface contains some normally liquid hydrocarbon compounds such as pentanes, gas wells usually produce some liquid hydrocarbons. In some cases, the quantities of liquid hydrocarbons produced from a gas well are too low to be measured. In these cases, the subsurface pool is referred to as 'dry gas' pool. In other cases, the quantities of normally liquid hydrocarbons in the subsurface gas are so great that the production at surface is dominantly liquid (see " 1920's: The Turner Valley Controversy "). If measurable quantities of liquid hydrocarbons are produced at surface from a gas well, the subsurface pool is referred to as a 'wet gas' pool.

A complete compositional spectrum of single phase conventional hydrocarbon pools exists with dry gas pools forming one end of the spectrum and heavy oil pools the other. If there are more normally gaseous hydrocarbons trapped in a subsurface pool than can be dissolved in the liquid hydrocarbons within the pool, the oil is said to be saturated with gas and both a liquid and a gaseous phase will exist in equilibrium in the pool. The gas phase, being lighter, will overly the 'oil leg' as a 'gas cap'. Due to the fact that oil was the focus of early exploration and development, such pools have come to be known as oil pools, irrespective of whether the gas cap or the oil leg is volumetrically larger or economically more valuable. The oil and gas 'pool' terminology may conjure up visions of vast subterranean caverns or lakes filled with oil or gas. In fact, subsurface hydrocarbons are normally found in the tiny voids or pores of subsurface rock formations. Even the solidest and most dense rocks have some internal void space or porosity. The degree to which this void space is connected so as to allow fluids to flow through the rock is referred to as the rock's 'permeability'.

It is generally accepted that oil and gas pools are formed when hydrocarbons migrating from areas of high hydrostatic pressure deep in the earth to areas of low pressure through porous and permeable rock formations over geological time encounter a permeability barrier which prevents their further migration and results in their becoming 'trapped'. When a well is drilled into a subsurface pool and perforated, pressure communication is effectively established between the surface and the subsurface and the equilibrium of the pool is disturbed. The pressure in the pool in the area immediately surrounding the well bore is reduced and this causes the oil or gas present in the pool to begin to flow toward the well bore through the tiny interstices connecting the voids or pores in the permeable reservoir rock formation. Oil and gas are referred to as fugacious minerals because of their ability to flow from one area of a subsurface pool to another in response to production-induced pressure differentials. It is this fugacious character, together with their non-unique chemical composition, which distinguishes oil and gas from hard minerals. End Notes: 1. Petroleum Reservoir Engineering, Amyx J.W., Bass D.M. and Whiting R.L., Texas A. & M., 1960, p.

295 Greenhouse Effect Factors affecting the Greenhouse Effect There are three main factors that directly influence the greenhouse effect: (1) the total energy influx from the sun, which depends on the earth's distance from the sun and on solar activity, (2) the chemical composition of the atmosphere (what gases are present and in what concentrations), and (3) albedo, the ability of the earth's surface to reflect light back into space. The only factor that has changed significantly in the last 100 years is the chemical composition of the atmosphere—and that is because of human activity. Human activity has changed the concentration of certain greenhouse gases in the atmosphere since the beginning of the Industrial Revolution, around 1750. The three graphs below show that the amounts of carbon dioxide (in parts per million), methane (in parts per billion) and nitrous oxide (in parts per billion) in the earth's atmosphere have increased dramatically over the past 1,000 years, with the most rapid increase occurring over the past fifty years.

Global warming: Anthropogenic (human-cased) forcing Although the greenhouse effect is a naturally-occurring process, humans have recently amplified the natural effect by increasing the concentration of CO2 and other greenhouse gases in the atmosphere (primarily through fossil fuel use in the energy and transportation sectors). According to the most recent report by the Intergovernmental Panel on Climate Change (IPCC’s 4th Assessment Report), there is greater than a 90% chance that human activity is causing the increase in Earth’s global average temperatures observed since the mid-21st century. The major greenhouse gases are listed in the figure below, along with their chemical formula. Although some of the gases listed have a larger global warming potential, carbon dioxide (CO2) is the most important greenhouse gas because of its abundance in the atmosphere. Today, atmospheric CO2 concentrations measure over 380 parts per million (ppm), mostly due to fossil fuel use in the energy and transportation sectors. Overview of Greenhouse Gases | Greenhouse Gas (GHG) Emissions | US EPA Overview of Greenhouse Gases Total Emissions in 2014 = 6,870 Million Metric Tons of CO2 equivalent .

Larger image to save or print. Gases that trap heat in the atmosphere are called greenhouse gases. This section provides information on emissions and removals of the main greenhouse gases to and from the atmosphere. For more information on the science of climate change and other climate forcers, such as black carbon, please visit Climate Change Science . 6,870 million metric tons of CO2: What does that mean? An explanation of units: A million metric tons is equal to about 2.2 billion pounds, or 1 trillion grams. For comparison, a small car is likely to weigh a little more than 1 metric ton. Thus, a million metric tons is roughly the same mass as 1 million small cars! The U.S. Inventory uses metric units for consistency and comparability with other countries. For reference, a metric ton is a little bit larger (about 10%) than a U.S. "short" ton. GHG emissions are often measured in carbon dioxide (CO2) equivalent. To convert emissions of a gas into CO2 equivalent, its emissions are multiplied by the gas's Global Warming Potential (GWP) .

The GWP takes into account the fact that many gases are more effective at warming Earth than CO2, per unit mass. The GWP values appearing in the Emissions webpages reflect the values used in the U.S. Inventory, which are drawn from the IPCC’s Fourth Assessment Report (AR4). For further discussion of GWPs and an estimate of GHG emissions using updated GWPs, see Annex 6 of the U.S. Inventory and the IPCC's discussion on GWPs . Exit Carbon dioxide (CO2) : Carbon dioxide enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and wood products, and also as a result of certain chemical reactions (e.g., manufacture of cement). Carbon dioxide is removed from the atmosphere (or "sequestered") when it is absorbed by plants as part of the biological carbon cycle. Methane (CH4) : Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.

Nitrous oxide (N2O) : Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste. Fluorinated gases : Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons). These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases, they are sometimes referred to as High Global Warming Potential gases ("High GWP gases"). Each gas's effect on climate change depends on three main factors: How much of these gases are in the atmosphere? Concentration, or abundance, is the amount of a particular gas in the air. Larger emissions of greenhouse gases lead to higher concentrations in the atmosphere. Greenhouse gas concentrations are measured in parts per million, parts per billion, and even parts per trillion.

One part per million is equivalent to one drop of water diluted into about 13 gallons of liquid (roughly the fuel tank of a compact car). To learn more about the increasing concentrations of greenhouse gases in the atmosphere, visit the Causes of Climate Change and the Climate Change Indicators: Atmospheric Concentrations of Greenhouse Gases pages. How long do they stay in the atmosphere? Each of these gases can remain in the atmosphere for different amounts of time, ranging from a few years to thousands of years. All of these gases remain in the atmosphere long enough to become well mixed, meaning that the amount that is measured in the atmosphere is roughly the same all over the world, regardless of the source of the emissions. How strongly do they impact global temperatures? Some gases are more effective than others at making the planet warmer and "thickening the Earth's blanket." For each greenhouse gas, a Global Warming Potential (GWP) has been calculated to reflect how long it remains in the atmosphere, on average, and how strongly it absorbs energy. Gases with a higher GWP absorb more energy, per pound, than gases with a lower GWP, and thus contribute more to warming Earth.

Global Warming Potential (100-year): 1 Carbon dioxide (CO2) is the primary greenhouse gas emitted through human activities. In 2014, CO2 accounted for about 80.9% of all U.S. greenhouse gas emissions from human activities. Carbon dioxide is naturally present in the atmosphere as part of the Earth's carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals). Human activities are altering the carbon cycle–both by adding more CO2 to the atmosphere and by influencing the ability of natural sinks, like forests, to remove CO2 from the atmosphere. While CO2 emissions come from a variety of natural sources, human-related emissions are responsible for the increase that has occurred in the atmosphere since the industrial revolution. 1 Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014 . Larger image to save or print. The main human activity that emits CO2 is the combustion of fossil fuels (coal, natural gas, and oil) for energy and transportation, although certain industrial processes and land-use changes also emit CO2.

The main sources of CO2 emissions in the United States are described below. Electricity . Electricity is a significant source of energy in the United States and is used to power homes, business, and industry. The combustion of fossil fuels to generate electricity is the largest single source of CO2 emissions in the nation, accounting for about 37 percent of total U.S. CO2 emissions and 30 percent of total U.S. greenhouse gas emissions in 2014. The type of fossil fuel used to generate electricity will emit different amounts of CO2. To produce a given amount of electricity, burning coal will produce more CO2 than oil or natural gas. Transportation . The combustion of fossil fuels such as gasoline and diesel to transport people and goods is the second largest source of CO2 emissions, accounting for about 31 percent of total U.S. CO2 emissions and 25 percent of total U.S. greenhouse gas emissions in 2014. This category includes transportation sources such as highway vehicles, air travel, marine transportation, and rail. Industry . Many industrial processes emit CO2 through fossil fuel combustion.

Several processes also produce CO2 emissions through chemical reactions that do not involve combustion; for example, the production and consumption of mineral products such as cement, the production of metals such as iron and steel, and the production of chemicals. Fossil fuel combustion from various industrial processes accounted for about 15 percent of total U.S. CO2 emissions and 12 percent of total U.S. greenhouse gas emissions in 2014. Note that many industrial processes also use electricity and therefore indirectly cause the emissions from the electricity production. Carbon dioxide is constantly being exchanged among the atmosphere, ocean, and land surface as it is both produced and absorbed by many microorganisms, plants, and animals. However, emissions and removal of CO2 by these natural processes tend to balance. Since the Industrial Revolution began around 1750, human activities have contributed substantially to climate change by adding CO2 and other heat-trapping gases to the atmosphere. In the United States, since 1990, the management of forests and non-agricultural land has acted as a net sink of CO2, which means that more CO2 is removed from the atmosphere, and stored in plants and trees, than is emitted.

This sink offset about 11 percent of total emissions in 2014 and is discussed in more detail in the Land Use, Land-Use Change, and Forestry section. To find out more about the role of CO2 warming the atmosphere and its sources, visit the Causes of Climate Change page and the Climate Change Indicators page in the Science section. Emissions and Trends Carbon dioxide (CO2) emissions in the United States increased by about 9 percent between 1990 and 2014. Since the combustion of fossil fuel is the largest source of greenhouse gas emissions in the United States, changes in emissions from fossil fuel combustion have historically been the dominant factor affecting total U.S. emission trends. Changes in CO2 emissions from fossil fuel combustion are influenced by many long-term and short-term factors, including population growth, economic growth, changing energy prices, new technologies, changing behavior, and seasonal temperatures. Between 1990 and 2014, the increase in CO2 emissions corresponded with increased energy use by an expanding economy and population, and an overall growth in emissions from electricity generation. Transportation emissions also contributed to the 9 percent increase, largely due to an increase in miles traveled by motor vehicles.

Larger image to save or print. Reducing Carbon Dioxide Emissions The most effective way to reduce carbon dioxide (CO2) emissions is to reduce fossil fuel consumption. Many strategies for reducing CO2 emissions from energy are cross-cutting and apply to homes, businesses, industry, and transportation. EPA is taking common sense regulatory actions to reduce greenhouse gas emissions from our nation's largest sources, including power plants and motor vehicles. Examples of How Emissions Can be Reduced Energy Efficiency Improving the insulation of buildings, traveling in more fuel-efficient vehicles, and using more efficient electrical appliances are all ways to reduce energy consumption, and thus CO2 emissions. See EPA's ENERGY STAR® program for more information on energy-efficient appliances. See EPA's and DOE's fueleconomy.gov site for more information on fuel-efficient vehicles. Learn about EPA's motor vehicle standards that improve vehicle efficiency and save drivers money. Energy Conservation Reducing personal energy use by turning off lights and electronics when not in use reduces electricity demand. Reducing distance traveled in vehicles reduces petroleum consumption. Both are ways to reduce energy CO2 emissions through conservation. Learn more about What You Can Do at Home , at School , in the Office , and on the Road to save energy and reduce your carbon footprint.

Fuel Switching Producing more energy from renewable sources and using fuels with lower carbon contents are ways to reduce carbon emissions. Carbon Capture and Sequestration Carbon dioxide capture and sequestration is a set of technologies that can potentially greatly reduce CO2 emissions from new and existing coal- and gas-fired power plants, industrial processes, and other stationary sources of CO2. Learn more . * Carbon dioxide's lifetime is poorly defined because the gas is not destroyed over time, but instead moves among different parts of the ocean-atmosphere-land system. Some of the excess carbon dioxide will be absorbed quickly (for example, by the ocean surface), but some will remain in the atmosphere for thousands of years, due in part to the very slow process by which carbon is transferred to ocean sediments. References Global Warming Potential (100-year): 25 Methane (CH4) is the second most prevalent greenhouse gas emitted in the United States from human activities. In 2014, CH4 accounted for about 11 percent of all U.S. greenhouse gas emissions from human activities. Methane is emitted by natural sources such as wetlands, as well as human activities such as leakage from natural gas systems and the raising of livestock.

Natural processes in soil and chemical reactions in the atmosphere help remove CH4 from the atmosphere. Methane's lifetime in the atmosphere is much shorter than carbon dioxide (CO2), but CH4 is more efficient at trapping radiation than CO2. Pound for pound, the comparative impact of CH4 on climate change is more than 25 times greater than CO2 over a 100-year period. Globally, over 60 percent of total CH4 emissions come from human activities. 1 Methane is emitted from industry, agriculture, and waste management activities, described below. Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014 . Larger image to save or print. Industry . Natural gas and petroleum systems are the largest source of CH4 emissions from industry in the United States. Methane is the primary component of natural gas. Some CH4 is emitted to the atmosphere during the production, processing, storage, transmission, and distribution of natural gas. Because gas is often found alongside petroleum, the production, refinement, transportation, and storage of crude oil is also a source of CH4 emissions.

For more information, see the Inventory of U.S. Greenhouse Gas Emissions and Sinks sections on Natural Gas Systems and Petroleum Systems. Agriculture . Domestic livestock such as cattle, buffalo, sheep, goats, and camels produce large amounts of CH4 as part of their normal digestive process. Also, when animals' manure is stored or managed in lagoons or holding tanks, CH4 is produced. Because humans raise these animals for food, the emissions are considered human-related. Globally, the Agriculture sector is the primary source of CH4 emissions. For more information, see the Inventory of U.S. Greenhouse Gas Emissions and Sinks Agriculture chapter. Waste from Homes and Businesses . Methane is generated in landfills as waste decomposes and in the treatment of wastewater. Landfills are the third largest source of CH4 emissions in the United States. For more information see the U.S. Inventory's Waste chapter. Methane is also emitted from a number of natural sources. Wetlands are the largest source, emitting CH4 from bacteria that decompose organic materials in the absence of oxygen. Smaller sources include termites, oceans, sediments, volcanoes, and wildfires.

To find out more about the role of CH4 in warming the atmosphere, and its sources, visit the Causes of Climate Change page and the Climate Change Indicators page in the Science section. Emissions and Trends Methane (CH4) emissions in the United States decreased by 6 percent between 1990 and 2014. During this time period, emissions increased from sources associated with agricultural activities, while emissions decreased from sources associated with the exploration and production of natural gas and petroleum products. Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2014 . These estimates use a global warming potential for methane of 25, based on reporting requirements under the United Nations Framework Convention on Climate Change. Larger image to save or print. Reducing Methane Emissions There are a number of ways to reduce methane (CH4) emissions. Some examples are discussed below. EPA has a series of voluntary programs for reducing CH4 emissions, and is supporting the president's Strategy to Reduce Methane Emissions (15 pp, 1.9 M, About PDF ).

EPA also supports the Global Methane Initiative Exit , an international partnership encouraging global methane reduction strategies. Examples of Reduction Opportunities for Methane Emissions Source How Emissions Can be Reduced Industry Upgrading the equipment used to produce, store, and transport oil and gas can reduce many of the leaks that contribute to CH4 emissions. Methane from coal mines can also be captured and used for energy. Learn more about the EPA's Natural Gas STAR Program and Coalbed Methane Outreach Program . Agriculture Methane can be reduced and captured by altering manure management strategies at livestock operations or animal feeding practices. Learn more about these strategies and EPA's AgSTAR Program . Waste from Homes and Businesses Because CH4 emissions from landfill gas are a major source of CH4 emissions in the United States, emission controls that capture landfill CH4 are an effective reduction strategy. Learn more about these opportunities and the EPA's Landfill Methane Outreach Program . References Global Warming Potential (100-year): 298 In 2014, nitrous oxide (N2O) accounted for about 6 percent of all U.S. greenhouse gas emissions from human activities.

Nitrous oxide is naturally present in the atmosphere as part of the Earth's nitrogen cycle, and has a variety of natural sources. However, human activities such as agriculture, fossil fuel combustion, wastewater management, and industrial processes are increasing the amount of N2O in the atmosphere. Nitrous oxide molecules stay in the atmosphere for an average of 114 years before being removed by a sink or destroyed through chemical reactions. The impact of 1 pound of N2O on warming the atmosphere is almost 300 times that of 1 pound of carbon dioxide. Globally, about 40 percent of total N2O emissions come from human activities. 1 Nitrous oxide is emitted from agriculture, transportation, and industry activities, described below. Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014 . Larger image to save or print. Agriculture . Nitrous oxide is emitted when people add nitrogen to the soil through the use of synthetic fertilizers. Agricultural soil management is the largest source of N2O emissions in the United States, accounting for about 79 percent of total U.S.

N2O emissions in 2014. Nitrous oxide is also emitted during the breakdown of nitrogen in livestock manure and urine, which contributed to 4 percent of N2O emissions in 2014. Transportation . Nitrous oxide is emitted when transportation fuels are burned. Motor vehicles, including passenger cars and trucks, are the primary source of N2O emissions from transportation. The amount of N2O emitted from transportation depends on the type of fuel and vehicle technology, maintenance, and operating practices. Industry . Nitrous oxide is generated as a byproduct during the production of nitric acid, which is used to make synthetic commercial fertilizer, and in the production of adipic acid, which is used to make fibers, like nylon, and other synthetic products. Nitrous oxide emissions occur naturally through many sources associated with the nitrogen cycle, which is the natural circulation of nitrogen among the atmosphere, plants, animals, and microorganisms that live in soil and water. Nitrogen takes on a variety of chemical forms throughout the nitrogen cycle, including N2O. Natural emissions of N2O are mainly from bacteria breaking down nitrogen in soils and the oceans.

Nitrous oxide is removed from the atmosphere when it is absorbed by certain types of bacteria or destroyed by ultraviolet radiation or chemical reactions. To find out more about the role of N2O in warming the atmosphere and its sources, visit the Causes of Climate Change page and the Climate Change Indicators page in the Science section. Emissions and Trends Nitrous oxide (N2O) emissions in the United States have decreased by 1 percent between 1990 and 2014. This decrease in emissions is due in part to a decrease in emissions from mobile combustion resulting from emission control standards for on-road vehicles. Nitrous oxide emissions from agricultural soils have varied during this period and were about 5 percent higher in 2014 than in 1990. Going forward, N2O emissions are projected to increase by 5 percent between 2005 and 2020, driven largely by increases in emissions from agricultural activities. 2 There are a number of ways to reduce emissions of nitrous oxide (N2O), discussed below.

Examples of Reduction Opportunities for Nitrous Oxide Emissions Emissions Source Examples of How Emissions Can be Reduced Agriculture The application of fertilizers accounts for the majority of N2O emissions. Emissions can be reduced by reducing nitrogen-based fertilizer applications and applying fertilizers more efficiently, 3 as well as following better manure management practices. Transportation Nitrous oxide is a byproduct of fuel combustion, so reducing mobile fuel consumption in motor vehicles can reduce transportation emissions. Additionally, the introduction of pollution control technologies, such as catalytic converters to reduce exhaust pollutants from passenger cars, can also reduce emissions of N2O. Industry Nitrous oxide is generally emitted from industry through fossil fuel combustion, so technological upgrades and fuel switching are effective ways to reduce industry emissions of N2O. Production of adipic acid results in N2O emissions that can be reduced through technological upgrades. References NF3: 17,200 SF6: 22,800 Unlike many other greenhouse gases, fluorinated gases have no natural sources and only come from human-related activities. They are emitted through a variety of industrial processes such as aluminum and semiconductor manufacturing.

Many fluorinated gases have very high global warming potentials (GWPs) relative to other greenhouse gases, so small atmospheric concentrations can have large effects on global temperatures. They can also have long atmospheric lifetimes—in some cases, lasting thousands of years. Like other long-lived greenhouse gases, fluorinated gases are well-mixed in the atmosphere, spreading around the world after they are emitted. Fluorinated gases are removed from the atmosphere only when they are destroyed by sunlight in the far upper atmosphere. In general, fluorinated gases are the most potent and longest lasting type of greenhouse gases emitted by human activities. There are four main categories of fluorinated gases—hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3). The largest sources of fluorinated gas emissions are described below. Larger image to save or print. Substitution for Ozone-Depleting Substances. Hydrofluorocarbons are used as refrigerants, aerosol propellants, solvents, and fire retardants.

The major emissions source of these compounds is their use as refrigerants—for example, in air conditioning systems in both vehicles and buildings. These chemicals were developed as a replacement for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) because they do not deplete the stratospheric ozone layer. Chlorofluorocarbons and HCFCs are being phased out under an international agreement, called the Montreal Protocol. Unfortunately, HFCs are potent greenhouse gases with long atmospheric lifetimes and high GWPs, and they are released into the atmosphere through leaks, servicing, and disposal of equipment in which they are used. Industry. Perfluorocarbons are compounds produced as a byproduct of various industrial processes associated with aluminum production and the manufacturing of semiconductors. Like HFCs, PFCs generally have long atmospheric lifetimes and high GWPs. Sulfur hexafluoride is used in magnesium processing and semiconductor manufacturing, as well as a tracer gas for leak detection. HFC-23 is produced as a byproduct of HCFC-22 production. Transmission and Distribution of Electricity.

Sulfur hexafluoride is used in electrical transmission equipment, including circuit breakers. The GWP of SF6 is 22,800, making it the most potent greenhouse gas that the Intergovernmental Panel on Climate Change has evaluated. To find out more about the role of fluorinated gases in warming the atmosphere, and their sources, visit the Causes of Climate Change page and the Climate Change Indicators page in the Science section. Emissions and Trends Overall, fluorinated gas emissions in the United States have increased by about 77 percent between 1990 and 2014. This increase has been driven by a 258 percent increase in emissions of hydrofluorocarbons (HFCs) since 1990, as they have been widely used as a substitute for ozone-depleting substances. Emissions of perfluorocarbons (PFCs) and sulfur hexafluoride (SF6) have actually declined during this time due to emission reduction efforts in the aluminum production industry (PFCs) and the electricity transmission and distribution industry (SF6).

Going forward, HFC emissions are projected to grow by nearly 141 percent between 2005 and 2020 as demands for refrigeration continue to grow and as more ozone-depleting substances are replaced. During this same period, emissions of SF6 are expected to decline by over 25 percent, while emissions of PFCs are projected to remain flat. Since the emissions from HFCs are far greater than the emissions of the other gases on a carbon dioxide-equivalence basis, substantial growth in emissions of fluorinated gases is expected to continue. 1 Larger image to save or print. Reducing Fluorinated Gas Emissions Because most fluorinated gases have a very long atmospheric lifetime, it will take many years to see a noticeable decline in current concentrations. However, there are a number of ways to reduce emissions of fluorinated gases, described below. Examples of Reduction Opportunities for Fluorinated Gases Emissions Source The PFC Reduction/Climate Partnership for the Semiconductor Industry Electricity Transmission and Distribution Sulfur hexafluoride is an extremely potent greenhouse gas that is used for several purposes when transmitting electricity through the power grid.

EPA is working with industry to reduce emissions through the SF6 Emission Reduction Partnership for Electric Power Systems , which promotes leak detection and repair, use of recycling equipment, and employee training. Transportation Hydrofluorocarbons (HFCs) are released through the leakage of refrigerants used in vehicle air-conditioning systems. Leakage can be reduced through better system components, and through the use of alternative refrigerants with lower global warming potentials than those presently used. One important way the EPA is working to reduce HFC emissions is through its light-duty and heavy-duty vehicle standards . References (10 pp, 577 K, About PDF ). U.S. Department of State, Washington, DC, USA. Methane | Wisconsin Department of Health Services Exposure Information Breathing Most exposures occur when people inhale methane. Methane can go into homes through sewer traps or foundation cracks. People can be exposed by inhaling the chemical at work, cooking on a gas stove, or entering confined spaces such as manholes, silos, animal waste pits, septic tanks and sewers. Drinking/Eating Because methane evaporates quickly, it is usually not found in food or drinking water.

Very low-level exposure can occur when contaminated water is used for drinking or food preparation or when children eat contaminated soil. Touching Methane gas does not pass readily through intact skin. Methane in its extremely cold liquefied form can, however, cause burns to the skin and eyes. Air/Water/Soil Standards Air Since it's a "simple asphyxiant," methane can displace available oxygen. There are no workplace limits for methane allowed in the air. No standards exist for the amount of methane allowed in the air of homes. The limiting factor is the amount of oxygen available. The minimum oxygen content in the home or workplace should be 18%. The Wisconsin Department of Natural Resources regulates the amount of methane that can be released by industries. Water There is currently no state or federal drinking water standard for methane. Contact your local public health department for more information specific to your situation. Health Effects Immediately or shortly after exposure to oxygen levels of less than 15% in air, a person may feel tired, dizzy, and have a headache. In general, a chemical will affect the same organ systems in all people who are exposed. However, the seriousness of the effects may vary from person to person.

A person's reaction depends on several things, including individual health, heredity, previous exposure to chemicals including medicines, and personal habits such as smoking or drinking. It’s also important to consider the length of exposure to the chemical, the amount of chemical exposure, and whether the chemical was inhaled, touched, or eaten. The following health effects can occur after several years of exposure to methane: Cancer

Question: What commonly occurring gas has the chemical formula CH4 ?
Answer: Methane