Articles | Volume 8, issue 17
Atmos. Chem. Phys., 8, 5373–5391, 2008
Atmos. Chem. Phys., 8, 5373–5391, 2008

  10 Sep 2008

10 Sep 2008

Photolysis frequency measurement techniques: results of a comparison within the ACCENT project

B. Bohn1, G. K. Corlett2, M. Gillmann3,*, S. Sanghavi3, G. Stange4, E. Tensing4, M. Vrekoussis5,**, W. J. Bloss6,***, L. J. Clapp7, M. Kortner8,****, H.-P. Dorn1, P. S. Monks2, U. Platt3, C. Plass-Dülmer4, N. Mihalopoulos5, D. E. Heard6, K. C. Clemitshaw7,*****, F. X. Meixner8, A. S. H. Prevot9, and R. Schmitt10 B. Bohn et al.
  • 1Institut für Chemie und Dynamik der Geosphäre 2: Troposphäre, Forschungszentrum Jülich, 52425 Jülich, Germany
  • 2Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK
  • 3Institut für Umweltphysik, Universität Heidelberg, 69120 Heidelberg, Germany
  • 4Deutscher Wetterdienst, Meteorologisches Observatorium Hohenpeissenberg, 82383 Hohenpeissenberg, Germany
  • 5Environmental Chemistry Laboratory, University of Crete, 71003 Voutes, Heraklion, Greece
  • 6School of Chemistry, University of Leeds, Leeds LS2 9JT, UK
  • 7Department of Environmental Science and Technology, Imperial College London, Silwood Park Campus, Ascot SL5 7PY, UK
  • 8Biogeochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 9Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
  • 10Meteorologie Consult GmbH (Metcon), 61462 Königstein, Germany
  • *now at: SIG Plasmax GmbH, 22145 Hamburg, Germany
  • **now at: Institut für Umweltphysik, University of Bremen, 28359 Bremen, Germany
  • ***now at: School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK
  • ****now at: Müller-BBM GmbH, 63589 Linsengericht, Germany
  • *****now at: Department of Earth Sciences, Royal Holloway, University of London, Egham TW20 0EX, UK

Abstract. An intercomparison of different radiometric techniques measuring atmospheric photolysis frequencies j(NO2), j(HCHO) and j(O1D) was carried out in a two-week field campaign in June 2005 at Jülich, Germany. Three double-monochromator based spectroradiometers (DM-SR), three single-monochromator based spectroradiometers with diode-array detectors (SM-SR) and seventeen filter radiometers (FR) (ten j(NO2)-FR, seven j(O1D)-FR) took part in this comparison. For j(NO2), all spectroradiometer results agreed within ±3%. For j(HCHO), agreement was slightly poorer between −8% and +4% of the DM-SR reference result. For the SM-SR deviations were explained by poorer spectral resolutions and lower accuracies caused by decreased sensitivities of the photodiode arrays in a wavelength range below 350 nm. For j(O1D), the results were more complex within +8% and −4% with increasing deviations towards larger solar zenith angles for the SM-SR. The direction and the magnitude of the deviations were dependent on the technique of background determination. All j(NO2)-FR showed good linearity with single calibration factors being sufficient to convert from output voltages to j(NO2). Measurements were feasible until sunset and comparison with previous calibrations showed good long-term stability. For the j(O1D)-FR, conversion from output voltages to j(O1D) needed calibration factors and correction functions considering the influences of total ozone column and elevation of the sun. All instruments showed good linearity at photolysis frequencies exceeding about 10% of maximum values. At larger solar zenith angles, the agreement was non-uniform with deviations explainable by insufficient correction functions. Comparison with previous calibrations for some j(O1D)-FR indicated drifts of calibration factors.

Final-revised paper