Technical Note: Formal blind intercomparison of OH measurements: results from the international campaign HOxComp 1Forschungszentrum Jülich, ICG-2: Troposphäre, 52425 Jülich, Germany
2Frontier Research Center for Global Change (currently Research Institute for Global Change), Japan Agency for Marine-Earth Science and Technology, Yokohama 236-0001, Japan
3Tokyo Metropolitan University, Department of Applied Chemistry, Tokyo 192-0397, Japan
4Max Planck Institute for Chemistry, Atmospheric Chemistry Dept., 55020 Mainz, Germany
5Deutscher Wetterdienst, Meteorol. Observatorium, 82383 Hohenpeissenberg, Germany
6Forschungszentrum Karlsruhe, IMK-AAF, 76021 Karlsruhe, Germany
*now at: National University of Ireland Galway, Department of Physics, Galway, Ireland
Received: 26 May 2009 – Published in Atmos. Chem. Phys. Discuss.: 26 June 2009 Abstract. Hydroxyl radicals (OH) are the major oxidizing species in the troposphere.
Because of their central importance, absolute measurements of their concentrations
are needed to validate chemical mechanisms of
atmospheric models. The extremely low and highly variable concentrations in the
troposphere, however, make measurements of OH difficult.
Three techniques are currently used worldwide for tropospheric observations of OH
after about 30~years of technical developments:
Differential Optical Laser Absorption Spectroscopy (DOAS),
Laser-Induced Fluorescence Spectroscopy (LIF),
and Chemical Ionisation Mass Spectrometry (CIMS).
Even though many measurement campaigns with OH data were published,
the question of accuracy and precision is still under discussion.
Revised: 16 September 2009 – Accepted: 23 September 2009 – Published: 22 October 2009
Here, we report results of the first formal, blind intercomparison
of these techniques. Six OH instruments (4~LIF, 1~CIMS, 1~DOAS)
participated successfully in the ground-based, international
HOxComp campaign carried out in Jülich, Germany, in summer 2005.
Comparisons were performed for three days in ambient air
(3~LIF, 1 CIMS) and for six days in the atmosphere
simulation chamber SAPHIR (3~LIF, 1~DOAS).
All instruments were found to measure tropospheric OH concentrations
with high sensitivity and good time resolution. The pairwise correlations
between different data sets were linear and yielded high
correlation coefficients (r2=0.75−0.96).
Excellent absolute agreement was observed for the instruments at the SAPHIR
chamber, yielding slopes between 1.01 and 1.13 in the linear
regressions. In ambient air, the slopes deviated from unity by
factors of 1.06 to 1.69, which can partly be explained by the
stated instrumental accuracies. In addition, sampling
inhomogeneities and calibration problems have apparently
contributed to the discrepancies. The absolute intercepts of the
linear regressions did not exceed 0.6×106 cm−3,
mostly being insignificant and of minor importance for
daytime observations of OH. No relevant interferences
with respect to ozone, water vapour, NOx and peroxy radicals
could be detected.
The HOxComp campaign has demonstrated that OH can
be measured reasonably well by current instruments,
but also that there is still room for improvement of calibrations.
Citation: Schlosser, E., Brauers, T., Dorn, H.-P., Fuchs, H., Häseler, R., Hofzumahaus, A., Holland, F., Wahner, A., Kanaya, Y., Kajii, Y., Miyamoto, K., Nishida, S., Watanabe, K., Yoshino, A., Kubistin, D., Martinez, M., Rudolf, M., Harder, H., Berresheim, H., Elste, T., Plass-Dülmer, C., Stange, G., and Schurath, U.: Technical Note: Formal blind intercomparison of OH measurements: results from the international campaign HOxComp, Atmos. Chem. Phys., 9, 7923-7948, doi:10.5194/acp-9-7923-2009, 2009.