Abstract

The hydroperoxyl radical (HO2) is one of the most abundant free radicals in the atmosphere, where it participates in a series of photochemical reactions that determine the fate of natural and anthropogenic emissions. In addition, HO2 is found in droplets and surface water as a result of photochemical formation and gas-phase scavenging. We describe a quantitative method for determining trace concentrations of HO2 radicals that exploits the chemiluminescence produced upon reaction with a synthetic analogue of luciferin from the crustacean Cypridina. The technique is linear at least up to 1 microM HO2(aq) and has a minimum detection limit of 0.1 nM. A unique feature of this analysis is a calibration method using stable aqueous HO2 standards produced in submicromolar concentrations using 60Co gamma-radiolysis. The advantage of this method in comparison to others in consideration of field deployment is its simplicity, low cost, and minimal size and power requirements. One intended application of this technique is the measurement of atmospheric HO2 radicals following collection into aqueous solution.