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Ambient formaldehyde concentrations are reported from the North AtlanticMarine Boundary Layer Experiment (NAMBLEX) campaign at Mace Head on the westcoast of Eire during August 2002. The results from two techniques, usingdirect determination via gas chromatography and the Hantzsch technique, showsimilar trends but a significant off set in concentrations. For westerly airflows characteristic of the marine boundary layer, formaldehydeconcentrations from the gas chromatographic and Hantzsch technique rangedfrom 0.78–1.15 ppb and 0.13–0.43 ppb, respectively. Possible reasonsfor the discrepancy have been investigated and are discussed, however, nosatisfactory explanation has yet been found. In a subsequent laboratoryintercomparison the two techniques were in good agreement.The observed concentrations have been compared with previous formaldehydemeasurements in the North Atlantic marine boundary layer and with othermeasurements from the NAMBLEX campaign. The measurements from the Hantzschtechnique and the GC results lie at the lower and upper ends respectively ofprevious measurements. In contrast to some previous measurements, bothtechniques show distinct diurnal profiles with day maxima and with anamplitude of approximately 0.15 ppb. Strong correlations were observed withethanal concentrations measured during NAMBLEX and the ratio of ethanal toformaldehyde determined by the gas chromatographic technique is in goodagreement with previous measurements.Some simple box modelling has been undertaken to investigate possiblesources of formaldehyde. Such models are not able to predict absoluteformaldehyde concentrations as they do not include transport processes, butthe results show that oxygenated VOCs such as ethanal and methanol are verysignificant sources of formaldehyde in the air masses reaching Mace Head

atmospheric chemistry and physics

Ambient formaldehyde measurements made at a remote marine boundary layer site during the NAMBLEX campaign – a comparison of data from chromatographic and modified Hantzsch techniques