Comparison of formaldehyde measurements by Hantzsch, CRDS and DOAS in the SAPHIR chamber

Abstract. Three instruments that use different techniques to measure gaseous formaldehyde (HCHO) concentrations were compared in experiments the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich. One instrument (AL4021, Aero-Laser GmbH) detects HCHO using wet-chemical Hantzsch reaction (for efficient gas-phase stripping), chemical conversion and fluorescence measurement. An internal permeation source allows for daily calibrations. This was characterized by sulfuric acid titration (overall accuracy 8.6 %) yields measurements with a time resolution of 90 s limit detection (3?) 0.3 ppbv. In addition, new commercial makes cavity ring-down spectroscopy (CRDS) determined HCHO, water vapour, methane (G2307, Picarro, Inc.). Its is specified as ppbv an integration 300 s, its limited drift zero signal (manufacturer specification 1.5 ppbv). A custom-built high-resolution laser differential optical absorption (DOAS) provided 0.9 7 %??????? multiple reflection cell. The conducted from June December 2019 which either ambient air flowed through or photochemical degradation organic compounds synthetic investigated. Measured up 8 Various mixtures compounds, nitrogen oxides ozone present these experiments. Results demonstrate need correct baseline performed compensate drifting background signals. Corrections equivalent mixing ratios range 0.5–1.5 CRDS showed linear dependence on vapour ratio slope (-11.20±1.60) %?1 below (-0.72±0.08) above 0.2 %. intercepts relationships drifted within (1.5 ppbv) over but appeared be equal all ratios. Regular are needed account changes zero. After correcting baselines instruments, regression analysis three indicated good agreement, slopes between 0.98 1.08 negligible (linear correlation coefficients R2>0.96). small measures precision accurate if taken into account. Therefore, it can provide similar DOAS slightly reduced instrument.