GEOCHEMISTRY: Night and Day, You Are the One

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Science  01 Apr 2005:
Vol. 308, Issue 5718, pp. 21a
DOI: 10.1126/science.308.5718.21a

The hydroxyl (OH) radical is a highly reactive atmospheric component that is involved in many important chemical reactions in the troposphere, particularly the oxidation of organic compounds. One important pathway for OH formation is the photolysis of nitrous acid (HONO), which accumulates in the lower troposphere at night and serves as a significant source of OH radicals in polluted air in the early morning. A daytime source of HONO has been proposed, on the basis of measurements showing higher-than-predicted HONO concentrations during the day.

Kleffmann et al. now report direct measurements of nitrous acid and hydroxyl radicals in the atmosphere at a forest site in Jülich, Germany. Their results establish the existence of an efficient daytime formation process for HONO, because they also measured the photolysis frequency of HONO, the other parameter needed to assess the size of the daytime HONO source. They conclude that HONO contributes substantially to the local primary OH production and that it may have an important influence on the oxidation of biogenic volatile organic compounds emitted by the forest. — HJS

Geophys. Res. Lett. 32, 10.1029/2005GL022524 (2005).

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