You can’t address methane without talking about hydroxyl radicals

Extracts from an article by the Regenetarianism blogger

When you look at the atmosphere, you don’t see anything – but it’s as complex as soil.

There are an infinite number of reactions going on with a whole wide array of trace gases and radicals, so atmospheric chemistry is quite complex – and you really can’t have a discussion of methane without a corresponding discussion of hydroxyl radicals (which break methane down), because the atmospheric chemistry is so interdependent.

With hydroxyl radicals, you have to look at how they’re utilized, their availability and their formation. That means you also have to look at where methane comes from. It comes from a myriad of sources, but there are three primary categories: thermogenic, biogenic and pyrogenic. Thermogenic includes sources like coal bed gas, fractured gas, natural gas – biogenic can be naturally occurring and caused by mankind (for example, rice is anthropogenic, but wetlands, which have similar dynamics, are naturally occurring) – and finally there’s pyrogenic, which is what’s released from fires.

These sources of methane are measured in different ways. You measure them via inventories that exist and you’re extrapolating. That’s called bottom-up analysis. Then there’s top down where you’re figuring out the carbon isotopic signatures in the atmosphere and trying to differentiate between different sources of emission based on those isotopologues.

The problem with bottom up is what’s easy to measure is usually what gets the blame. For example, enteric methane from cattle is easy to measure with chambers, mask, and SF6 tracers. Such measurements are out of ecosystem context. It’s treating cattle like exhaust pipes.

Top down is only as good as the inventory of signatures, and there’s a lot of overlap with signatures. Plus the old thinking was that methane came strictly from methanogenic archaea in anoxic, anaerobic environments. But that thinking is a little outdated, because now researchers realize that methane pretty much comes from everything, including bacteria, eukaryotes and archaea. These all emit methane, and there is a lot of variability in their carbon signatures. So when you’re trying to figure out where methane comes from based on isotopic signatures, sometimes, sources are misread or misattributed because there’s so much overlap.

While methane comes from a myriad of sources, everybody points their finger at cattle. And what’s kind of ironic is if you’re if you have this net zero mentality and you want to really cool the earth, you have to rehydrate the earth as well. But, if you rehydrate the earth (and we have 250m beaver ponds in North America), you’re actually massively increasing methane emissions.

A lot of recent growth in methane emissions has been due to increased wetland emissions and a decrease in hydroxyl radical availability. So this is why you also really have to understand methane sinks to understand methane dynamics.

Thus you can’t discuss methane emissions without also discussing methane sinks providing offsets.

You have a relatively small sink with soil methanotrophic bacteria. They help. If you have saprophytic fungi decomposing organic mass in a compost pile or in dirt, the methane they emit won’t make it into the atmosphere if you have methanotrophic bacteria. This will oxidize methane emitted in the soil before the methane gets into the atmosphere. A similar thing happens with termites in a mound. The methane never really gets released or escapes from the mound into the atmosphere because the methane emitted by the termites is oxidized before it escapes from the termite mound.

But the bigger sink is the tropospheric sink which is the lowest part of the atmosphere up to about thirty miles or so above the earth. When methane is emitted here, most is eventually oxidized back via a long process mainly to CO2 and water vapour.

Most people say the lifespan of CH4 is nine, ten or twelve years or something like that. But that figure is a median average and it’s gone up since pre-industrialization from about approximately five point nine years to nine point two years. But again that’s the median.

When you get up into the stratosphere, it can take methane up to one-hundred and forty years to break down. But if hydroxyl radicals are available, methane can be broken down very quickly. So methane persistence or lack of persistence is all dependent upon hydroxyl radical availability.

Hydroxyl radicals last for less than a second. That’s why they’re so difficult to measure and there’s so much uncertainty about the size of the tropospheric methane sink. So, it’s not like hydroxyl radicals hang around for nine years to interact with methane and methane doesn’t magically break down by itself. Methane needs to have one of its hydrogen’s stolen by a hydroxyl radical, which has a negative charge.

With hydroxyl oxidation, there are a lot of interactions. And with industrialization, there’s both more methane and fewer hydroxyl radicals. So there’s more methane from burning fossil fuels and from fugitive emissions. And at the same time when you combust coal, gas and other fossil fuels, there’s also more competition particularly from carbon monoxide [which hydroxyl radicals also help to break down].

And what’s needed for hydroxyl radical formation via the primary pathway is tropospheric ozone. That primary pathway is when tropospheric ozone is zapped by light below a certain wavelength (photolysis). This releases oxygen and an excited oxygen atom. That excited oxygen, in turn, interacts with water vapour to form two hydroxyl radicals.

Plant transpiration is also part of the process. So, in addition to transpired water vapour, another part of the equation are biological volatile organic compounds like isoprene and pinene that are emitted from the stomata of leaves of plants. Thus if you have desertification or are in a feed lot, you’re not going to have those components to form hydroxyl radicals and therefore methane is going to hit the troposphere and stay there for awhile. If there aren’t any hydroxyl radicals to collide with, the methane emitted will be more persistent.

So where cattle are grazing and emitting methane among plants in a green zone (an area of a lush grassland environment with lots of plants doing a lot of photosynthesis cycling), the plants and soil are also emitting all the precursors needed to form the surface level ozone, water vapour, nitric oxide, nitrates, etc to create hydroxyl radicals. Thus this is an ecosystem where sources of methane and methane sinks balance out.

If you’re in a feedlot, and the feeds have been grown with a lot of synthetic nitrogen, there aren’t any precursors and so no hydroxyl radicals form. Methane sources and sinks don’t balance out.

Also, if cattle are being raised on deforested land in the Amazon or some other similar environment, you’re reducing precursor emissions, and thus weakening the cycle. So again, the ecosystem doesn’t balance out. So all methane generation is context specific.

Regenerative Ag and its umbrella of practices help to reconnect people to land and repair these disrupted out of balance cycles. Regenerative agriculture, regenerative agroforestry and regenerative agroecology are all under this umbrella of regenerative Ag. The key word is regenerative that’s both a noun and a verb. We have to regenerate both terrestrial and aquatic ecosystems. The real dichotomy is between regenerative versus degenerative systems of food production not plants versus meat.

Read the full, referenced blog here


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