The Oxidizing Capacity of the Earth's Atmosphere: Probable Past and Future Changes

TLDR

The lower atmosphere’s oxidizing capacity is dominated by ozone, hydroxyl radicals, and hydrogen peroxide, and its global burden is critical for many chemical processes, though model validation remains early. Evidence for changes in Earth’s oxidizing capacity since the preindustrial era is limited, but ozone and possibly hydrogen peroxide concentrations have risen regionally, and models project a 0.3–1 % per year increase in tropospheric ozone over the next 50 years with uncertain trends for OH and H₂O₂.

Abstract

The principal oxidants in the lower atmosphere are ozone (O 3 ) and two by-products of O 3 photodissociation, the hydroxyl radical (OH) and hydrogen peroxide (H 2 O 2 ). A number of critical atmospheric chemical problems depend on the earth's "oxidizing capacity," which is essentially the global burden of these oxidants. There is limited direct evidence for changes in the earth's oxidizing capacity since recent preindustrial times when, because of industrial and population growth, increasing amounts of O 3 precursor trace gases (carbon monoxide, nitrogen oxides, and hydrocarbons) have been released into the atmosphere. The concentrations of O 3 and possibly H 2 O 2 have increased over large regions. Models predict that tropospheric O 3 will increase ∼0.3 to 1% per year over the next 50 years with both positive and negative trends possible for OH and H 2 O 2 . Models and the observational network for oxidants are improving, but validation of global models is still at an early stage.