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

Abstract

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

Atmospheric photooxidation and ozonolysis of Δ<sup>3</sup>-carene and 3-caronaldehyde: rate constants and product yields

“…On a global scale, the emission of carbon from biogenic volatile organic compounds (BVOCs) exceeds 1000 Tg per year (Guenther et al, 2012). Among all BVOC emissions, monoterpenes are the second most important class of species, contributing up to 16 % to the total emissions.…”

Evaluation of Aeris MIRA, Picarro CRDS G2307, and DNPH-based sampling for long-term formaldehyde monitoring efforts

“…The operating principle of cavity ringdown spectroscopy as used by the G2307 is described fully in Glowania et al (2021), and briefly summarized here. Air is pulled through a temperature and pressure-controlled cavity at a rate of 120 0.4 standard liters per minute (SLPM).…”

“…In recent years, several 65 commercially available instruments have been developed towards that goal, including a cavity ring down spectroscopy (CRDS) instrument from Picarro, a photoacoustic gas analyser from Gasera, and Tunable Diode Laser Spectroscopy (TDLS) instruments from Aeris Technologies and Aerodyne Research, Inc. Here, we focus on the Aeris MIRA and Picarro CRDS G2307 instruments, which have been compared against other instruments in a small number of informal (Whitehill et al, 2018;Furdyna, 2020) and peer-reviewed (Shutter et al, 2019;Glowania et al, 2021) intercomparison efforts. Since those efforts, the Picarro G2307 instrument implemented updates to its spectral fitting algorithm, and the Aeris MIRA instrument has offered improved thermal stabilization.…”

“…Whitehill et al (2018) found an inverse correlation between Picarro HCHO measurements and instrument-reported water mixing ratios at typical, ambient concentrations and, along with Furdyna (2020), observed that the G2307's measurements were lower by 1-2 ppb HCHO compared to DNPH-based measurements. Glowania et al (2021), using a spectral fitting algorithm 85 updated after the Whitehill et al (2018) intercomparison (released Sep. 2019, found that low humidity conditions can lead to changes in reported HCHO concentrations as high as 1.75 ppb. These offsets are most significant at ≤ 0.2% H2O where the H2O spectral feature is not clearly observed.…”

Investigation of the limonene photooxidation by OH at different NO concentrations in the atmospheric simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction Chamber)

“…Measurements of formaldehyde (HCHO) concentrations were available from either one of three instruments which included an instrument making use of the Hantzsch reaction (AL4021, Aero Laser GmbH), the DOAS instrument that is also used for the detection of OH, and a cavity ring-down spectroscopy (CRDS) analyzer (Picarro G2307) (Glowania et al, 2021). Measurements using the Hantzsch method were available in the experiments in 2012, measurements with DOAS were available in the experiments in 2015, and measurements with CRDS were available in the experiments in 2019.…”