Intercomparison of four different in-situ techniques for ambient formaldehyde measurements in urban air

Abstract

Abstract.Results from an intercomparison of several currently used in-situ techniques for the measurement of atmospheric formaldehyde (CH 2 O) are presented. The measurements were carried out at Bresso, an urban site in the periphery of Milan (Italy) as part of the FORMAT-I field campaign. Eight instruments were employed by six independent research groups using four different techniques: Differential Optical Absorption Spectroscopy (DOAS), Fourier Transform Infra Red (FTIR) interferometry, the fluorimetric Hantzsch reaction technique (five instruments) and a chromatographic technique employing C18-DNPH-cartridges (2,4-dinitrophenylhydrazine). White type multi-reflection systems were employed for the optical techniques in order to avoid spatial CH 2 O gradients and ensure the sampling of nearly the same air mass by all instruments. Between 23 and 31 July 2002, up to 13 ppbv of CH 2 O were observed. The concentrations lay well above the detection limits of all instruments. The formaldehyde concentrations determined with DOAS, FTIR and the Hantzsch instruments were found to agree within ±11%, with the exception of one Hantzsch instrument, which gave systematically higher values. The two hour integrated samples by DNPH yielded up to 25% lower concentrations than the data of the continuously measuring instruments averaged over the same time period. TheCorrespondence to: C. Hak (claudia.hak@iup.uni-heidelberg.de) consistency between the DOAS and the Hantzsch method was better than during previous intercomparisons in ambient air with slopes of the regression line not significantly differing from one. The differences between the individual Hantzsch instruments could be attributed in part to the calibration standards used. Possible systematic errors of the methods are discussed.

The formaldehyde budget as seen by a global-scale multi-constraint and multi-species inversion system

“…However, these first studies did not use any HCHO observations. Indeed, large disagreements exist between the various measurement techniques employed for measuring HCHO mixing ratios (spectroscopic, chromatographic, and fluorimetric) (Hak et al, 2005). As a result, there is not yet a consistent global measurement network for HCHO as it exists for greenhouse gases or other air pollutants such as CO, CH 4 and ozone.…”

Intercomparison of open-path trace gas measurements with two dual-frequency-comb spectrometers

“…Similar intercomparison measurements between conventional active open-path sensors are rare but have shown agreement of typically 1-20 % (Thoma et al, 2005;Hak et al, 2005;Smith et al, 2011;Shao et al, 2013;Conde et al, 2014;Reiche et al, 2014;Thalman et al, 2015). Here, we find agreement between two DCS instruments that is an order of magnitude better and is comparable to that achieved with highly calibrated, state-of-the-art solar-looking FTS systems that retrieve vertical column measurements (Messerschmidt et al, 2011;Frey et al, 2015;Hedelius et al, 2016); how-ever, open-path DCS does not require instrument-specific calibrations (e.g., of the instrument line shape) and provides a very different capability by retrieving the dry mole fractions across regional, kilometer-scale paths over day and night on a mobile platform.…”

A new non-resonant laser-induced fluorescence instrument for the airborne in situ measurement of formaldehyde

“…In addition to airborne observations, total column HCHO is measured by satellite (Chance et al, 2000;Steck et al, 2008), making HCHO one of the few VOCs observable from space. Numerous measurement technique reviews and instrument intercomparisons are available (Fried et al, 2008a;Hak et al, 2005;Kaiser et al, 2014;Zhu et al, 2016).…”