ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-10-21189-2010 Technical Note: Formal blind intercomparison of HO<sub>2</sub> measurements in the atmosphere simulation chamber SAPHIR during the HOxComp campaign Fuchs H. 1 Brauers T. 1 Dorn H.-P. 1 Harder H. 2 Häseler R. 1 Hofzumahaus A. 1 Holland F. 1 Kanaya Y. 3 Kajii Y. 4 Kubistin D. 2 Lou S. 1 5 Martinez M. 2 Miyamoto K. 4 Nishida S. 4 Rudolf M. 2 Schlosser E. 1 7 Wahner A. 1 Yoshino A. 4 Schurath U. 6 Forschungszentrum Jülich, ICG-2: Troposphäre, 52425 Jülich, Germany Max Planck Institute for Chemistry, Atmospheric Chemistry Department, 55020 Mainz, Germany Frontier Research Center for Global Change (currently Research Institute for Global Change), Japan Agency for Marine-Earth Science and Technology, Yokohama, 236-0001, Japan Tokyo Metropolitan University, Department of Applied Chemistry, Tokyo 192-0397, Japan Shanghai Jiatong University, School of Environmental Science and Technology, Shanghai, China Karlsruhe Institute of Technology (KIT), IMK-AAF, 76021 Karlsruhe, Germany now at: Karlsruhe Institute of Technology (KIT), IMK-AAF, 76021 Karlsruhe, Germany 06 09 2010 10 9 21189 21235 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-discuss.net/10/21189/2010/acpd-10-21189-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/21189/2010/acpd-10-21189-2010.pdf

Hydroperoxy radical (HO<sub>2</sub>) concentrations were measured during the formal blind intercomparison campaign HOxComp carried out in Jülich, Germany. Three instruments detected HO<sub>2</sub> via chemical conversion to hydroxyl radicals (OH) and subsequent detection of the sum of OH and HO<sub>2</sub> by laser induced fluorescence (LIF). Instruments sampled ambient air for three days and were attached to the atmosphere simulation chamber SAPHIR during the second part of the campaign. Six experiments of one day each were conducted in SAPHIR, where air masses were homogeneously mixed, in order to investigate the performance of instruments and to determine potential interferences of measurements under well-controlled conditions. Linear correlation coefficients between measurements of the LIF instruments are generally high and range from 0.82 to 0.98. However, the agreement between measurements is variable. The regression analysis of the entire data set of measurements in SAPHIR yields slopes between 0.69 to 1.26 and intercepts are smaller than typical atmospheric daytime concentrations (less than 1 pptv). The quality of fit parameters improves significantly, when data are grouped into data subsets of similar water vapor concentrations. Because measurements of LIF instruments were corrected for a well-characterized water dependence of their sensitivities, this indicates that an unknown factor related to water vapor affected measurements in SAPHIR. Measurements in ambient air are also well correlated, but regression parameters differ from results obtained from SAPHIR experiments. This is most likely caused by sampling different air masses at the slightly distant locations of instruments.

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