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Emissions accounting of methane[edit]
Various sources give the following values for methane emissions:

Removal processes[edit]
Any process that consumes methane from the atmosphere can be considered a "sink" of atmospheric methane. The most prominent of these processes occur as a result of methane either being destroyed in the atmosphere or broken down in soil. Humans have yet to act as any significant sink of atmospheric methane.

Reaction with the hydroxyl radical – The major removal mechanism of methane from the atmosphere involves radical chemistry; it reacts with the hydroxyl radical (·OH) in the troposphere or stratosphere to create the ·CH3 radical and water vapor. In addition to being the largest known sink for atmospheric methane, this reaction is one of the most important sources of water vapor in the upper atmosphere. Following the reaction of methane with the hydroxyl radical, two dominant pathways of methane oxidation exist: [1] which leads to a net production of ozone, and [2] which causes no net ozone change. For methane oxidation to take the pathway that leads to net ozone production, nitric oxide (NO) must be available to react with CH3O2·. Otherwise, CH3O2· reacts with the hydroperoxyl radical (HO2·), and the oxidation takes the pathway with no net ozone change. Both oxidation pathways lead to a net production of formaldehyde and water vapor.

[1] Net production of O3

CH4 + ·OH → CH3· + H2O

CH3· + O2 + M → CH3O2· + M

CH3O2· + NO → NO2 + CH3O·

CH3O· + O2 → HO2· + HCHO

HO2· + NO → NO2 + ·OH

(2x) NO2 + hv → O(3P) + NO

(2x) O(3P) + O2 + M → O3 + M

[NET: CH4 + 4O2 → HCHO + 2O3 + H2O]

[2] No net change of O3

CH4 + ·OH → CH3· + H2O

CH3· + O2 + M → CH3O2· + M

CH3O2· + HO2· + M → CH3O2H + O2 + M

CH3O2H + hv → CH3O· + ·OH

CH3O· + O2 → HO2· + HCHO

[NET: CH4 + O2 → HCHO + H2O]

Note that for the second reaction, there will be a net loss of radicals in the case where CH3O2H is lost to wet deposition before it can undergo photolysis such that: CH3O2H + H2O → wet deposition. Also note that M represents a random molecule that facilitates energy transfer during the reaction.

Gas Chromatography
Methane is typically measured using gas chromatography. Gas chromatography is a type of chromatography used for separating or analyzing chemical compounds. It is less expensive in general, compared to more advanced methods, but it is more time and labor intensive.

Spectroscopic method
Spectroscopic methods are the preferred method for atmospheric gas measurements due to its sensitivity and precision. Also, spectroscopic methods are the only way of remotely sensing the atmospheric gases. Infrared spectroscopy covers a large spectrum of techniques, one of which detects gases based on absorption spectroscopy. There are various methods for spectroscopic methods, including Differential Optical Absorption Spectroscopy, Laser-Induced Fluorescence, and Fourier Transform Infrared.

====Cavity Ring-Down Spectroscopy ==== Cavity Ring-Down Spectroscopy is most widely used IR absorption technique of detecting methane. It is a form of laser absorption spectroscopy which determines the mole fraction to the order of parts per trillion.