Description:

Tropospheric oxidation is fundamental to both climate and air quality outcomes, and is driven primarily by hydroxyl radicals and to a lesser extent by halogen (e.g., chlorine) radicals. Methane, the second most important greenhouse gas, has an atmospheric lifetime of ~10 years primarily due to tropospheric oxidation as the main methane sink, so any changes to the tropospheric radical concentration will directly impact methane’s concentration and thus the climate. Tropospheric oxidation also influences tropospheric ozone, which is both a greenhouse gas and criteria air pollutant that is detrimental to human health and crop yields.

The tropospheric oxidation capacity is determined by complex, nonlinear atmospheric chemistry influenced by anthropogenic emissions, as well as evolving climate feedbacks. Some tropospheric species, such as carbon monoxide and hydrogen, compete with methane for hydroxyl radicals and are therefore indirect greenhouse gases. Reducing the emissions of both direct and indirect greenhouse gases will have climate and air quality implications, but the spatial variability, outcomes, and trajectories of these impacts are not yet well understood. Other, even less understood potential emissions – such as intentional enhancement of hydrogen peroxide or iron salt aerosols – could also influence the tropospheric oxidation capacity. Detailed laboratory, modeling, and field studies are required to better understand tropospheric oxidation and its systems level impacts on climate and air quality.