Recycling in the Earth's Atmosphere: The OH Radical—Its Importance for the Chemistry of the Atmosphere and the Determination of Its Concentration

The troposphere, the part of the earth's atmosphere which is closest to the surface, harbors important life processes. This important part of our environment contains primarily nitrogen and oxygen. In addition, it comprises a number of other substances, which are generally present in low concentrations. The primary reason for the low content of these trace components is the activity of a diatomic radical, namely the hydroxyl radical. OH is the main constituent of the oxidizing potential of the troposphere and causes the transformation of many trace components into water‐soluble forms, which can then rain out and be removed from the troposphere. OH has therefore acquired the title “detergent of the atmosphere”. The knowledge of local hydroxyl radical concentrations is therefore an important piece of information, especially with respect to model calculations for atmospheric chemistry. The OH concentration is very low and its determination represents a significant analytical challenge. It is controlled in a delicate manner by chemical formation and decomposition reactions, which interact to create a recycling process in the troposphere.