On the relative absorption strengths of water vapour in theblue wavelength range

[摘要] In recent updates of the HITRAN water vapour H₂O spectroscopiccompilation covering the blue spectral region (here: 394–480 nm)significant changes for the absorption bands at 416 and 426 nm werereported. In order to investigate the consistency of the differentcross-sections calculated from these compilations, H₂O vapour columndensity ratios for different spectral intervals were retrieved from long-pathand multi-axis differential optical absorption spectroscopy (DOAS)measurements. We observed a significant improvement of the DOAS evaluationwhen using the updated HITRAN water vapour absorption cross-sections for thecalculation of the reference spectra. In particular the magnitudes of theresidual spectra as well as the fit errors were reduced.

However, we also found that the best match between measurement and model isreached when the absorption cross-section of groups of lines are scaled byfactors ranging from 0.5 to 1.9, suggesting that the HITRAN water vapourabsorption compilation still needs significant corrections. For this spectralregion we present correction factors for HITRAN 2009, HITRAN 2012, HITEMP andBT2 derived from field measurements. Additionally, upper limits for watervapour absorption in the UV-A range from 330 to 390 nm are given.

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