Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 3 6 2003 10.5194/acpd-3-6029-2003 http://www.atmos-chem-phys-discuss.net/3/6029/2003/ http://www.atmos-chem-phys-discuss.net/3/6029/2003/acpd-3-6029-2003.html http://www.atmos-chem-phys-discuss.net/3/6029/2003/acpd-3-6029-2003.pdf 6029 6061 2003-11-28 Validation of the calibration of a laser-induced fluorescence instrument for the measurement of OH radicals in the atmosphere W. J. Bloss J. D. Lee C. Bloss K. Wirtz M. Martin-Reviejo M. Siese D. E. Heard M. J. Pilling Department of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK Fundación CEAM, EUPHORE Laboratories, C/Charles Darwin 14, Parque Technológico, 46980 Paterna, Valencia, Spain Institut für Chemie und Dynamik der Geosphäre, Institut II: Troposphäre, Forschungszentrum Jülich, D-52425 Jülich, Germany An assessment of the accuracy of OH concentrations measured in a smog chamber by a calibrated laser-induced fluorescence (LIF) instrument has been made, in the course of 9 experiments performed to study the photo-oxidation of benzene, toluene, 1,3,5-trimethylbenzene, para-xylene, ortho-cresol and ethene at the European Photoreactor facility (EUPHORE). The LIF system was calibrated via the water photolysis/ozone actinometry approach. OH concentrations were inferred from the instantaneous rate of removal of each hydrocarbon species (measured by FTIR or HPLC) via the appropriate rate coefficient for their reaction with OH, and compared with those obtained from the LIF system. Good agreement between the two approaches was found for all species with the exception of 1,3,5-trimethylbenzene, for which OH concentrations inferred from hydrocarbon removal were a factor of 3 lower than those measured by the LIF system. From the remaining 8 experiments, an overall value of 1.15±0.13 (±1σ) was obtained for [OH]_LIF/[OH]_{Hydrocarbon Decay}, compared with the estimated uncertainty in the accuracy of the water photolysis/ozone actinometry OH calibration technique of 26% (1σ)