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Enhanced Atmospheric Methane Removal

Definition
Enhanced atmospheric methane oxidation (EAMO) is a proposed method to enhance the natural process of atmospheric methane oxidation. It is a case of biomimicry.

Atmospheric methane has increased since pre-industrial times from 0.7 ppm to 1.9 ppm (CN). Methane is the cause of ca. 30% (0.5 °C) of current global warming (CN).

Atmospheric Methane Oxidation is a natural process which occurs in the atmosphere under sunny conditions in the presence of a catalyzer (CN). The process oxidises methane (CH4) into carbon dioxide and water.

1 CH4 + 2 O2 => 1 CO2 + 2 H2O

The catalyzer, in 95% of all cases, is  •OH, in 2-3% of all cases FeCl3. (CN)

Chemistry of Methane Removal
Most atmospheric methane is removed in nature by OH radicals. In EAMO the catalyzer FeCl3 (Iron-III chloride) is used because chlorine atoms (radicals) oxidize methane at least 16 times faster than OH[1]. Chlorine atoms are produced, for example, by photolysis from the Iron(III) chloride (FeCl3) content of hydrous airborne dust aerosol particles[2] in the oceanic boundary layer:

FeCl3 + hv  à  FeCl2 + oCl

Methane oxidation is initiated by the chlorine atoms:

CH4 + oCl  à HCl + oCH3

The resulting methyl radical is unstable and oxidises naturally to CO2 and water:

3.5O2 + 2oCH3 à 2CO2 + 3H2O

Additional Benefits
Particles dispersed in the atmosphere can serve as CCN (Cloud Condensation Nuclei) and thereby cause Marine Cloud Brightening (MCB).

Eventually all FeCl3 particles are washed out of the air by precipitation and fall on land or water, where they dissolve into Iron compounds and salt (CN). EAMO would contribute to Iron Fertilization of both the sea and the land. Since the particles are widely distributed before they hit the ocean the effect per square-meter would be miniscule in comparison to sea-level OIF.

[1] Baker et al., (2016): Evidence for strong, widespread chemistry associated with pollution outflow from continental Asia. Scientific reports, 6, 36821, doi: 10.1038/srep36821 (See table 2, page 4)

[2] Oeste FD, de Richter R, Ming T, Caillol S (2017): Climate engineering by mimicking natural dust climate control: the iron salt aerosol method. Earth System Dynamics, 8, 1-54, doi: 10.5194/esd-8-1-2017