Towards an Optical Gas Standard for Traceable Calibration-Free and Direct NO2 Concentration Measurements

We report a direct tunable diode laser absorption spectroscopy (dTDLAS) instrument developed for NO2 concentration measurements without chemical pre-conversion, operated as an Optical Gas Standard (OGS). An OGS is dTDLAS that can deliver gas species amount fractions (concentrations), any previous or routine calibration, which are directly traceable to the international system of units (SI). Here, we fraction quantification in range 100–1000 µmol/mol demonstrate current capability car exhaust application. Nitrogen dioxide results delivered by good agreement with certified values reference mixtures, validating dTDLAS-OGS calibration-free measurements. As opposed standard method (SRM) based on chemiluminescence detection (CLD) where indirectly measured after conversion NO, titration O3 and resulting fluorescence, has benefit measuring distorting delaying processes. Therefore, it complements SRM perform fast measurements, side-by-side calibrations other analyzers operating field. The relative uncertainty reported this paper 5.1% (k = 1, dominated (98%) line strength), repeatability at 982.6 0.1%, response time 0.5 s, limit 825 nmol/mol resolution 86 s.