THE RADIOCHEMICAL HYDROXYL RADICAL MEASUREMENT METHOD

The radiocarbon tracer technique for measuring ground-level OH concentrations is described in detail with special emphasis on the validity of the method and the steps taken to ensure reproducible measurements. The method uses 14CO as a tracer of the tropospheric CO-OH reaction in a photolytic UV-transparent flow reactor. The OH concentration is inferred from the amount of tracer used, the CO-OH reaction rate constant, the reaction time, and the β− activity of the resulting 14CO2. Forty-two experiments performed on 5 days in October 1987 revealed midday mean OH concentrations of (10.1 ± 3.3) × 106 and (2.9 ± 0.5) × 106 radicals cm−3 in polluted and pure air, respectively. Early morning and evening OH concentrations were less than (2.5 ± 0.5) × 105 radicals cm−3. The significant differences between the OH concentrations observed in the clean air near Colfax, WA, and the polluted air in Pullman, WA, are attributed to the Washington State University coal-fired power plant plume. © 1990, American Chemical Society. All rights reserved.