Development of a measurement system of peroxy radicals using a chemical amplification/laser-induced fluorescence technique

Abstract

An instrument for measuring atmospheric peroxy radicals has been developed by chemical amplification/laser-induced fluorescence (PERCA/LIF) technique. The small concentration of peroxy radicals is converted to the large amount of NO2, which is measured by laser-induced fluorescence instead of luminol chemiluminescence. Several advantages, that is, high sensitivity, high selectively, and fast time response, are expected by use of LIF for the NO2 measurement, in comparison with luminol chemiluminescence. When using this system, simultaneous measurements of NO2 and peroxy radicals are available. The present optimum condition for the reaction tube (1/4 in. Teflon) was determined to be the reaction tube length of 3 m, the NO and CO concentrations of 3 ppmv and 10%, respectively. The calibration, including humidity dependence of the detection sensitivity of peroxy radicals, was conducted and the present detection limit of peroxy radicals was determined to be 2.7 and 3.6 pptv at the ambient relative humidity of 50 and 80%, respectively, for the integration time of 1 min (S/N=2). This detection limit was calculated assuming the ambient O3 and NO2 mixing ratios of 30 and 20 ppbv, respectively. The influence of the NO2 detection sensitivity by adding high concentrations of CO was investigated and the quenching of excited NO2 by CO can affect the ambient measurement significantly under the high NO2 and low peroxy radical concentrations. Exploratory ambient air measurements were made in suburban area of Osaka, Japan. These results demonstrated the performance of PERCA/LIF for ambient measurements.