Intercomparison of formaldehyde measurements in clean and polluted atmospheres

Three different techniques used to measure atmospheric formaldehyde were co mpared during a field campaign carried out at a clean maritime site on the West coast of Ireland. Two spectroscopic techniques Differential Optical Ab sorption Spectroscopy (DOAS) and Tunable Diode Laser Absorption Spectroscop y (TDLAS), together with a glass coil/Hantzsch reaction/fluorescence techni que, were employed for measurements of atmospheric formaldehyde of the orde r of a few hundred pptv. The better agreement was observed between the fluo rescence and DOAS instruments. Two DOAS instruments were compared to the glass coil/Hantzsch reaction/fluo rescence 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 wer e also deployed simultaneously in order to measure indoor air inside a mobi le 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 emissio ns. 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 techniq ue proved the most suitable for continuous measurements of formaldehyde in the background atmosphere.