Intercomparison of formaldehyde measurements in clean and polluted atmospheres

Three different techniques used to measure atmospheric formaldehyde were compared during a field campaign carried out at a clean maritime site on the West coast of Ireland. Two spectroscopic techniques Differential Optical Absorption Spectroscopy (DOAS) and Tunable Diode Laser Absorption Spectroscopy (TDLAS), together with a glass coil/Hantzsch reaction/fluorescence technique, were employed for measurements of atmospheric formaldehyde of the order of a few hundred pptv. The better agreement was observed between the fluorescence and DOAS instruments. Two DOAS instruments were compared to the glass coil/Hantzsch reaction/fluorescence technique at a semi-polluted site on the North Norfolk coast, U.K., where concentrations of formaldehyde were observed at levels up to 4 ppbv. A very good agreement was observed between the two instruments. The glass coil/Hantzsch reaction/fluorescence and the TDLAS instruments were also deployed simultaneously in order to measure indoor air inside a mobile laboratory located at the Imperial College Silwood Park site near Ascot, U.K. The doors of the mobile laboratory were left open in order to obtain the background formaldehyde concentrations. Closing them afterwards allowed us to observe the increase in concentrations as a result of indoor emissions. The agreement between the two instruments was outstanding (correlation coefficient was 99%). The results from this study showed that of the four instruments included in this intercomparison the glass coil/Hantzsch reaction/fluorescence technique proved the most suitable for continuous measurements of formaldehyde in the background atmosphere.