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

B. Bohn (1) , G. K. Corlett (2) , M. Gillmann (3) , S. Sanghavi (3) , G. Stange (4) , E. Tensing (4) , M. Vrekoussis (5) , W. J. Bloss (6) , L. J. Clapp (7) , M. Kortner (8) , H.-P. Dorn (1) , P. S. Monks (2) , U. Platt (3) , C. Plass-Dülmer (4) , N. Mihalopoulos (5) , D. E. Heard (6) , K. C. Clemitshaw (7) , F. X. Meixner (8) , A. S. H. Prevot (9) , R. Schmitt (10)

1 ICG-2 - Institut für Chemie und Dynamik der Geosphäre - Troposphäre
2 Department of Chemistry
3 Institut für Umweltphysik [Heidelberg]
4 DWD - Deutscher Wetterdienst [Offenbach]
5 Environmental Chemistry Laboratory [Crete]
6 School of Chemistry
7 Department of Environmental Science and Technology
8 Biogeochemistry Department [Mainz]
9 LAC - Laboratory of Atmospheric Chemistry [Paul Scherrer Institute]
10 Metcon - Meteorologie Consult GmbH

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 altitude 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.

Domaines: Océan, Atmosphère

B. Bohn, G. K. Corlett, M. Gillmann, S. Sanghavi, G. Stange, et al.. Photolysis frequency measurement techniques: results of a comparison within the ACCENT project. Atmospheric Chemistry and Physics Discussions, 2008, 8 (3), pp.10301-10352. ⟨hal-00304218⟩