Jun 27, 2022

In this video I delve into the details of the hydroxyl radical (OH*). This extremely reactive molecule is known as the “detergent of the atmosphere” and is the major scrubber of methane in the atmosphere.

Methane levels in the atmosphere are rapidly rising, with 2020 and 2021 being record setting years, by far. Since the Global Warming Potential (GWP) of methane is 34x that of CO2 on a 100 year timescale, a huge 86x on a 20 year timescale, and a whopping 150x to 200x on a year or two timescale, the record rise in methane is contributing enormously to abrupt climate system change.

Thus, knowing the details of the OH* molecule in the atmospheric are crucial for figuring out what to do to try and mitigate the atmospheric methane.

Short wavelength solar radiation in the Ultraviolet (UV; wavelength shorter than about 336 nm) has enough energy to break apart the ozone molecule into an O ion and an oxygen molecule. The extremely reactive O singlet reacts with water in the atmosphere to produce the OH. Thus, the concentration of OH is very high in the tropics which have lots of penetrating UV (low stratospheric ozone) and large water vapour concentrations (very hot Sea Surface Temperatures (SST) with lots of evaporation).

Since methane is rapidly rising, people thought that OH* would be depleted, but fortunately the OH* production (from ozone breakdown, water vapour reactions, reactions with NOx, widening of the Hadley Cell by between 0.5 to 1.0 degrees latitude per decade) are almost cancelling out the OH* loss from methane destruction chemical reactions. Some good news for a change; hopefully it continues.

Ref: Detergent-like Molecule Recycles Itself in Atmosphere (yr 2000).

Ref2: Study Discovers That This Methane Depleting Atmospheric Molecule Can Recycle Itself, Katarina Samurović, January 29, 2019

Ref: Global Monitoring Laboratory, Global CH4 Monthly Means

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