Measurements of the Diurnal OH Cycle by a super(14)C-Tracer Method

The hydroxyl free radical is considered the primary oxidant for the removal of pollutants from the atmosphere. The carbon 14-tracer technique was used to measure five ambient diurnal hydroxyl radical concentration cycles in relatively pure and in polluted air. The early- to mid-October maximum midday hydroxyl radical concentrations were 2.4 10 super(6) radicals/cu cm for pure air, and 9.5 10 super(6) radicals/cu cm for polluted air. Nighttime hydroxyl radical concentrations of less than 2 10 super(5) radicals/cu cm were measured. The estimates of hydroxyl radical concentrations from photochemical models and trace gas lifetimes are consistent with these observations.