Comparison of N2O5 mixing ratios during NO3Comp 2007 in SAPHIR

[摘要] N₂O₅ detection in the atmosphere has been accomplished usingtechniques which have been developed during the last decade. Most techniquesuse a heated inlet to thermally decompose N₂O₅ to NO₃, whichcan be detected by either cavity based absorption at 662 nm or bylaser-induced fluorescence. In summer 2007, a large set of instruments, whichwere capable of measuring NO₃ mixing ratios, were simultaneouslydeployed in the atmosphere simulation chamber SAPHIR in Jülich, Germany.Some of these instruments measured N₂O₅ mixing ratios eithersimultaneously or alternatively. Experiments focused on the investigation ofpotential interferences from, e.g., water vapour or aerosol and on theinvestigation of the oxidation of biogenic volatile organic compounds byNO₃. The comparison of N₂O₅ mixing ratios shows an excellentagreement between measurements of instruments applying different techniques(3 cavity ring-down (CRDS) instruments, 2 laser-induced fluorescence (LIF)instruments). Datasets are highly correlated as indicated by the square ofthe linear correlation coefficients, R², which values were larger than0.96 for the entire datasets. N₂O₅ mixing ratios well agree withinthe combined accuracy of measurements. Slopes of the linear regression rangebetween 0.87 and 1.26 and intercepts are negligible. The most critical aspectof N₂O₅ measurements by cavity ring-down instruments is thedetermination of the inlet and filter transmission efficiency. Measurementshere show that the N₂O₅ inlet transmission efficiency can decreasein the presence of high aerosol loads, and that frequent filter/inletchanging is necessary to quantitatively sample N₂O₅ in someenvironments. The analysis of data also demonstrates that a generalcorrection for degrading filter transmission is not applicable for allconditions encountered during this campaign. Besides the effect of a gradualdegradation of the inlet transmission efficiency aerosol exposure, no otherinterference for N₂O₅ measurements is found.

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