Confidence is Growing in Tropospheric OH Measurements

There aren't many hydroxyl molecules (OH) in the troposphere, but the few that are there certainly make their presence known. More than any other species in the troposphere (the atmospheric layer between Earth's surface and an altitude of 8–18 km), the OH radical determines the lifetimes of such common atmospheric constituents as carbon monoxide, methane and sulfur dioxide. Yet, because of its short atmospheric lifetime (a single molecule sticks around less than one second) and low concentrations (a few tenths of a part per trillion, compared, for example to carbon dioxide levels, which are a few hundred parts per million), the OH radical has defied accurate measurement. Not any more.