| Odd hydrogen radicals play an important role in nearly every chemical cycle of the atmosphere. Of particular current interest are tropospheric ozone production (catalyzed by NO(,x), CO, and CH(,4)) and acid rain formation. Hydroxyl radicals (HO) react with NO(,2) to form nitric acid, and begin a sequence which converts SO(,2) to sulfuric acid. The hydroperoxy radical (HO(,2)) reacts with NO to form NO(,2), thus allowing ozone to build up from oxygen atoms produced by NO(,2) photolysis. Development of measurement techniques for free radicals is important to improving our understanding of the chemistry of the atmosphere.;HO(,2) + NO (--->) NO(,2) + HO (1).;HO + CO (--->) H + CO(,2) (2).;H + O(,2) + M (--->) HO(,2) + M (3).;Our new technique for PEroxy Radical measurement by Chemical Amplification (PERCA) takes advantage of the chain reaction in which peroxy (e.g. HO(,2)) and oxy- (e.g. HO) radicals catalize the air oxidation of NO and CO: (UNFORMATTED TABLE FOLLOWS).;(TABLE ENDS).;This chain reaction forms 1100 NO(,2) molecules in 4.2 seconds for each HO(,x) (HO(,2) + HO) entering the system. Typical reagent concentrations are 3 ppmv for NO and 10% by volume for CO. The NO(,2) generated from the chain reaction is differentiated from ambient NO(,2), and NO(,2) from NO + O(,3) by substituting N(,2) for CO at a fixed frequency and measuring the NO(,2) modulation. The NO(,2) is detected by observing the photons produced from a gas-liquid surface chemiluminescence reaction with a basic aqueous luminol solution.;Calibration is accomplished by monitoring the second order decay of HO(,2) radicals generated by various techniques in the laboratory. Dividing the accepted rate constant for 2HO(,2) (--->) H(,2)O(,2) + O(,2) by the slope of the inverse radical signal versus decay time, yields the instrumental HO(,2) sensitivity. Some field measurements and a smog chamber study have been performed which demonstrate the feasibility of the method. Potential interferences using this technique are also discussed. |
