Development of a measurement system of OH reactivity in the atmosphere by using a laser-induced pump and probe technique

A novel instrument for measuring OH reactivity in the troposphere has been developed by using a laser-induced pump and probe technique. Air was introduced into a flow tube and OH was produced artificially using O-3 photolysis by 266 nm laser. The OH decay rate in the flow tube was monitored by the time-resolved laser-induced fluorescence technique. In this article, the instrument, that is, the measurement principle, the flow tube and the fluorescence detection cell, is presented in detail. Interference by absorption of the 266 nm laser light by O-3, and photolysis of NO2 and HCHO was found to be negligible. The influence of recycled OH from the HO2+NO reaction on the measured OH reactivity was estimated by a box model calculation. The systematic error of the measured decay rate was found to be less than 5% even in high NO condition ([NO]=20 ppbv). The dependence of the measured decay rate on the flow rate in the reaction tube was investigated. A slight change in the total flow rate does not influence the measured decay rate in our experimental condition. The second-order rate coefficients of the OH+CO reactions were measured in order to confirm the accuracy of the measured OH decay rate. The measured rate coefficients were agreed excellently with the recent recommended values. The results of observations in our institute are briefly presented. (C) 2004 American Institute of Physics.