Technical Note: Intercomparison of formaldehyde measurements at the atmosphere simulation chamber SAPHIR
The atmosphere simulation chamber SAPHIR at the Research Centre J¨ ulich was used to test the suitability of state-of-the-art analytical instruments for the measurement of gas-phase formaldehyde (HCHO) in air. Five analyzers based on four different sensing principles were deployed: a differential optical absorption spectrometer (DOAS), car- tridges for 2,4-dinitrophenylhydrazine (DNPH) derivatiza- tion followed by off-line high pressure liquid chromatogra- phy (HPLC) analysis, two different types of commercially available wet chemical sensors based on Hantzsch fluorime- try, and a proton-transfer-reaction mass spectrometer (PTR- MS). A new optimized mode of operation was used for the PTR-MS instrument which significantly enhanced its perfor- mance for online HCHO detection at low absolute humidi- ties. The instruments were challenged with typical ambient lev- els of HCHO ranging from zero to several ppb. Synthetic air of high purity and particulate-filtered ambient air were used as sample matrices in the atmosphere simulation chamber onto which HCHO was spiked under varying levels of hu- midity and ozone. Measurements were compared to mixing ratios calculated from the chamber volume and the known amount of HCHO injected into the chamber; measurements were also compared between the different instruments. The formal and blind intercomparison exercise was conducted under the control of an independent referee. A number of analytical problems associated with the experimental set-up and with individual instruments were identified, the overall agreement between the methods was fair.