Hydroxyl radical

hydroxyl radical

The hydroxyl radical, OH, is responsible for the oxidation of most of the compounds that are released into, or formed in, the atmosphere.

It is ubiquitous in the atmosphere, although its mean concentration is about 10⁶cm^-3 and the mixing ratio seldom exceeds 1 ppt (1 part in 10¹²). In the lower atmosphere it is formed by the reaction of excited oxygen atoms O(¹D) with water or by the reaction of hydroperoxyl radicals with nitric oxide. In the stratosphere it is involved in ozone-destroying catalytic cycles. The capacity of the atmosphere to clean itself via the occurrence of oxidation reactions (oxidizing capacity) is usually related to the level of OH present.

Levy, H. 1972. Photochemistry of the lower troposphere. Planet. Space Sci.. 20. 919–935.

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1. A gaseous envelope gravitationally bound to a celestial body (e.g., a planet, its satellite, or a star).