Formaldehyde Comparison (CRDS, DOAS, Hantzsch) SAPHIR chamber 2019

Three instruments using different techniques were used to measure gaseous formaldehyde (HCHO) concentrations in experiments in the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich. One instrument detected HCHO by using the wet-chemical Hantzsch reaction for efficient gas stripping, chemical conversion and fluorescence measurement (AL4021, Aero Laser GmbH). An internal permeation gas source provides daily calibrations characterized by sulfuric acid titration (accuracy 5%). Measurements have a time resolution of 90s with a limit of detection (3-sigma) of 0.3 ppbv. In addition, a new commercial instrument making use of cavity ring-down spectroscopy (CRDS) determined concentrations of HCHO, water, and methane (G2307, Picarro Inc.). The limit of detection (3-sigma) is specified as 0.3 ppbv for an integration time of 300s and the accuracy is limited by the drift of the zero (manufacturer specification 1.5 ppbv). A custom-built, high-resolution laser differential optical absorption spectroscopy (DOAS) instrument provided HCHO measurements with a limit of detection (3-sigma) of 0.9 ppbv and an accuracy of 10% using an optical multiple reflection cell. The measurements were conducted from June to December 2019 in experiments in which ambient air was flowed through the chamber and also in experiments investigating the photochemical degradation of organic compounds in synthetic air. The data set contains HCHO measurements of all three instruments together with chamber parameters (temperature, pressure) and the water mixing ratio needed to correct CRDS measurements.