Validation of the calibration of a laser-induced fluorescence instrument for the measurement of OH radicals in the atmosphere

摘要

An assessment of the accuracy of OH concentrations measured in a smogchamber by a calibrated laser-induced fluorescence (LIF) instrument has beenmade, in the course of 9 experiments performed to study the photo-oxidationof benzene, toluene, 1,3,5-trimethylbenzene, para-xylene, ortho-cresol and ethene atthe European Photoreactor facility (EUPHORE). The LIF system was calibratedvia the water photolysis / ozone actinometry approach. OH concentrations wereinferred from the instantaneous rate of removal of each hydrocarbon species(measured by FTIR or HPLC) via the appropriate rate coefficient for theirreaction with OH, and compared with those obtained from the LIF system. Goodagreement between the two approaches was found for all species with theexception of 1,3,5-trimethylbenzene, for which OH concentrations inferredfrom hydrocarbon removal were a factor of 3 lower than those measured by theLIF system. From the remaining 8 experiments, an overall value of 1.15±0.13 (±1σ) was obtained for [OH] / [OH], compared with the estimated uncertainty in the accuracy of thewater photolysis / ozone actinometry OH calibration technique of 26% (1σ).