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

An intercomparison of different radiometric techniques measuring atmospheric photolysis frequencies j (NO2), j (HCHO) and j (O 1 D) was carried out in a two- week field campaign in June 2005 at JGermany. Three double-monochromator based spectroradiometers (DM-SR), three single-monochromator based spectroradiometers with diode-array detectors (SM-SR) and seventeen filter radiome- ters (FR) (ten j (NO2)-FR, seven j (O 1 D)-FR) took part in this comparison. For j (NO2), all spectroradiometer re- sults agreed within ±3%. For j (HCHO), agreement was slightly poorer between 8% and +4% of the DM-SR ref- erence 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 wave- length range below 350 nm. For j (O 1 D), the results were