ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-571-2004 Validation of the calibration of a laser-induced fluorescence instrument for the measurement of OH radicals in the atmosphere Bloss W. J. 1 Lee J. D. 1 Bloss C. 1 Heard D. E. 1 Pilling M. J. 1 Wirtz K. 2 Martin-Reviejo M. 2 Siese M. 3 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 08 04 2004 4 2 571 583 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/4/571/2004/acp-4-571-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/571/2004/acp-4-571-2004.pdf

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&plusmn;0.13 (&plusmn;1&sigma;) was obtained for [OH]<sub>LIF</sub> / [OH]<sub>Hydrocarbon Decay</sub>, compared with the estimated uncertainty in the accuracy of the water photolysis / ozone actinometry OH calibration technique of 26% (1&sigma;).