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

[摘要] An intercomparison of different radiometric techniques measuring atmospheric photolysisfrequencies j(NO₂), j(HCHO) and j(O¹D) was carried outin a two-week field campaign in June 2005 at Jülich, Germany.Three double-monochromator based spectroradiometers (DM-SR), threesingle-monochromator based spectroradiometers with diode-arraydetectors (SM-SR) and seventeen filter radiometers (FR) (tenj(NO₂)-FR, seven j(O¹D)-FR) took part in thiscomparison. For j(NO₂), all spectroradiometer results agreedwithin ±3%. For j(HCHO), agreement was slightly poorerbetween −8% and +4% of the DM-SR reference result. For theSM-SR deviations were explained by poorer spectral resolutions andlower accuracies caused by decreased sensitivities of thephotodiode arrays in a wavelength range below 350 nm. Forj(O¹D), the results were more complex within +8% and−4% with increasing deviations towards larger solar zenithangles for the SM-SR. The direction and the magnitude of thedeviations were dependent on the technique of backgrounddetermination. All j(NO₂)-FR showed good linearity withsingle calibration factors being sufficient to convert from outputvoltages to j(NO₂). Measurements were feasible until sunsetand comparison with previous calibrations showed good long-termstability. For the j(O¹D)-FR, conversion from output voltagesto j(O¹D) needed calibration factors and correction functionsconsidering the influences of total ozone column and elevation ofthe sun. All instruments showed good linearity at photolysisfrequencies exceeding about 10% of maximum values. At largersolar zenith angles, the agreement was non-uniform with deviationsexplainable by insufficient correction functions. Comparison withprevious calibrations for some j(O¹D)-FR indicated drifts ofcalibration factors.

[学科分类] 大气科学