Atmospheric Oxidation Enhancement with chlorine atoms: Efficiency, Plume Dynamics, and New Mechanistic Insights

Methane is a powerful greenhouse gas, currently responsible for 0.5 degrees of warming. Because methane acts on a short timescale, reducing its emissions can limit temperature in the coming decades. However, rising global methane emissions highlight the need for enhanced efforts. In addition to methane emissions reduction, a new field of Atmospheric Oxidation Enhancement (AOE) is emerging that may reduce climate risks by artificially accelerating the natural breakdown of methane in the atmosphere.

Recent studies of atmospheric oxidation enhancement (AOE) involving chlorine atoms have relied on simplified assumptions, such as constant surface fluxes of reactive chlorine, or a catalytic iron-salt-aerosol efficiency that is independent of environmental parameters. While such studies highlight the scale of potential effects, these parameterizations obscure key issues of catalytic efficiency and deployment feasibility. Disagreement between global model parameterizations for iron-salt-aerosol exacerbates the problem of resolving these issues and can lead to contradictory conclusions.  Here we present independent lines of reasoning—based on elementary reaction kinetics, modelling, laboratory studies, and field analyses—that demonstrate the complexity that needs to be considered to assess the viability of AOE involving chlorine atoms. We show that effective deployment depends critically on location and conditions—sunlight, aerosol acidity, sea spray, background species (NOx, O3, acids, oxidants) and dispersion. In this context, plumes emerge as a distinct and attractive reactor class: local, temporary (days), and capable of entraining and processing large air volumes. Finally, we present recent advances in monitoring of enhanced atmospheric methane oxidation. This creates a route towards field studies providing data to validate models, and towards MRV approaches to validate hypothetical future atmospheric methane removal.