WTF happens to all that methane?

Okay this one is a bit nerdy, so I apologize in advance. When I’m not so lazy, I’ll track down all the scientific references, but for now I just want to summarize all of these compiled processes in what follows below. 

Methane emitted from a number of various sources doesn’t just rise into atmosphere unabated. That methane is actually always in the process of being broken down via a process called oxidation. In soils, what oxidizes microbial methane (made by single celled prokaryotes called methanogenic archaea) before it can get into the atmosphere are bacteria called methanotrophs. Once in the atmosphere, these bacteria still oxidize a small amount of this methane, but not a whole lot: Maybe around five percent.

methane sinks

However, once methane is in the atmosphere this is where all the real oxidation happens. This is where methane [CH4] collides with hydroxyl radicals and is ultimately reduced back to water H2O and cyclical CO2. Note the word cyclical since most atmospheric CO2 cycles via photosynthesis to glucose and oxygen O2 as a by product whether it goes through a human, a head of cattle or a kangaroo.

ch4 oxidation in troposphere

What basically happens is that with continuous diverse plant covers in pastures with plants and forests with trees,  there’s more transpiration from plants. That transpiration is water vapor. Water vapor interacts with excited oxygen to form 2 hydroxyl radicals as follow O (+) + H2O = 2OH-. OH- is the hydroxyl radical molecule.
The excited oxygen comes from, the photolysis of tropospheric ozone O3. Basically photolysis means that the ozone is zapped by UV light within a certain wavelength so O3 zapped by UV —> O2 + O(+). The O2 is atmospheric oxygen, That UV light is within a certain bandwidth (around 300 nm) so it’s more available at certain latitudes where stratospheric ozone is thinner.
Tropospheric ozone is usually considered “bad” while stratospheric ozone is considered “good”. Tropospheric ozone is basically smog in urban communities formed by the photolysis at a different wavelength of light of nitrates emitted from tailpipes and smoke stacks. So this low lying ozone is considered a pollutant.
However, tropospheric ozone can also be formed via BVOC’s . A BVOC is a biogenic volatile organic compound….specifically monoterpines which are released by heat stressed plants from their stomata (pores on the undersides of the plants leaves) . Trees release one form of monoterpines called isoprene while plants release other forms including pinene.

These monoterpines then react with nitric oxide released from soil to form longer nitrates …then those nitrates are zapped with light via photolysis to form ozone O3 which then is zapped as noted above and combined with water vapor to form the hydroxyl radicals. Those radicals are negatively charged free radicals that steal one of the hydrogens off of a CH4 molecule which starts a long process of breaking down CH4 to essentially H2O and cyclical CO2. as per the attached diagram (Figure 23 above).

trace gas removal

Hydroxyl radicals bind with other trace gas pollutants as well as also shown in the attachment. Almost all CH4 emitted is oxidized by OH in the geosphere, troposphere and stratosphere. Though CH4 oxidation in the troposphere is impacted by other trace gases like carbon monoxide, since the other trace gases use up some of the available hydroxyl radicals.


Anyway, as a interesting side note, the BVOC’s also interact with the hydroxyl radicals and  these oxidized BVOC’s then become the nuclei required for rain cloud formation, so trees and plants actually help produce rain.

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