Laundry Days | Methane and Hydroxyl Radicals
Following up on The Guardian’s recent article about the importance of Hydroxyl Radicals (OH) and the role they play as detergents in our atmosphere we decided to dig a little deeper. Whilst we did not find any answers to our ending questing, we would love to hear your thoughts on it.
Despite a pandemic-induced slowdown in anthropogenic activities emitting CH4, the compound’s presence in the atmosphere has increased significantly in the last 2 years. This prompted Simon Redfern and his team at Nanyang Technological University in Singapore to dig deeper.
By looking at historic methane measurements Redfern and his team posit that OH, which are a dominant sink of CH4, are being satiated by additional Carbon Monoxide (CO), possibly released by forest fires, thus leaving CH4 to persist harmfully in the troposphere.
OHs react more readily with CO, within a matter of months, as opposed to the decades OHs take to react with CH4.
Persisting CH4 thus exacerbates positive feedback loops and increases warming which promotes microbial activity in wetlands and the likelihood of wildfires which in turn emit more CH4, carbon dioxide (CO2) and most importantly CO. Hence, repeating the vicious cycle. The same warming which is increasing CH4 emissions is also reducing the potential for CH4 to be decomposed, removed from the atmosphere and prevented from performing its warming activity.
Widely referred to as a “detergent” or “nature’s most powerful cleaning agent”, OH are commonly used in air filters, hospitals and schools for their ability to neutralise bacteria, viruses, harmful gases, mould, and respiratory allergens. Taking into account these properties and the key role OH plays in closing the global methane budget one can only look at them as a potential mitigation technology.
Furthermore, a NASA study from 2018 hypothesises that breakdown products from the reaction with CH4 and OH could in fact react with Nitrous Oxides (NO) to reform the OHs, effectively recycling them. However, Redfern’s findings seem to suggest no significant recycling is occurring.
OH are formed via photolysis when ultraviolet sunlight reacts with water vapour (H2O) and ozone (O3) in the lower atmosphere. With such highly reactive properties they tend to react as soon as they are formed which has rendered quantification difficult.
Geoengineering is a highly contentious proposal with many risks and in some cases clear inverse effects such as the increased longevity of CH4 in the atmosphere caused by stratospheric aerosol injection (SAI).
Could further research into the promotion of OH production in the atmosphere yield some global warming mitigation technologies?
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Sources -
[1] Methane much more sensitive to global heating than previously thought — study | Greenhouse gas emissions | The Guardian
[2] Detergent-like Molecule Recycles Itself in Atmosphere
[3] Hydroxyl Radicals Clean Air Solutions | Axair Fans UK
[4] Large uncertainties in global hydroxyl projections tied to fate of reactive nitrogen and carbon | PNAS
[5] Hydroxyl and methane? SRM proponents fail to consider key aspect of atmospheric chemistry — Geoengineering Monitor
[6] The hunt for hydroxyl radicals in Antarctica could reveal the secrets of our future climate — ABC News (Australian Broadcasting Corporation)
[7] Hydroxyl Radical — an overview | ScienceDirect Topics
[8] www.atmosphere.mpg.de-oxidation-and-OH-radicals.pdf
[9] Hydroxyl Radical (OH) Response to Meteorological Forcing and Implication for the Methane Budget — He — 2021 — Geophysical Research Letters — Wiley Online Library
