OHRadikalen

OHRadikalen, in German-language literature often written as OH-Radikalen or OH•, refers to the hydroxyl radical, a highly reactive diatomic species composed of one oxygen and one hydrogen atom with an unpaired electron. It is a short-lived radical that typically exists only for milliseconds to seconds in many environments. The OH radical is considered a primary oxidant in the troposphere and plays a central role in initiating the oxidation of numerous organic and inorganic molecules.

In the atmosphere, the dominant formation pathway stems from the photolysis of ozone and the subsequent reaction of the produced excited oxygen O(1D) with water: O(1D) + H2O -> 2 OH. Other significant sources include photolysis of hydrogen peroxide and formaldehyde, as well as reactions involving excited atomic oxygen. In laboratory and environmental contexts, OH can also be generated by radiolysis or photolysis of water and hydrogen peroxide. Once formed, OH rapidly reacts with nearby species due to its high reactivity.

OH radicals initiate and sustain oxidation chains by abstracting hydrogen atoms from hydrocarbons and other substrates, generating water and organic radicals that propagate further reactions. These processes control the lifetimes of many atmospheric trace gases, influence the fate of pollutants, and contribute to secondary organic aerosol formation, thereby affecting air quality and climate. Their reactivity makes them valuable but difficult-to-study targets in both atmospheric and combustion chemistry.

Detection and measurement of OH radicals employ techniques such as laser-induced fluorescence (LIF), often at around 308 nm, cavity ring-down spectroscopy, and chemiluminescence. In the field, differential optical absorption spectroscopy and other spectroscopic methods are used to estimate OH concentrations in the atmosphere.

OHRadikalen are a cornerstone of environmental chemistry, bridging atmospheric processes, air quality, and climate dynamics.