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 T. J. Still1, S. Al-Haider1, P. W. Seakins1, R. Sommariva1, J. C. Stanton1, G. Mills2, and S. A. Penkett2 1School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK 2School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
Abstract. Ambient formaldehyde concentrations are reported from the North Atlantic
Marine Boundary Layer Experiment (NAMBLEX) campaign at Mace Head on the west
coast of Eire during August 2002. The results from two techniques, using
direct determination via gas chromatography and the Hantzsch technique, show
similar trends but a significant off set in concentrations. For westerly air
flows characteristic of the marine boundary layer, formaldehyde
concentrations from the gas chromatographic and Hantzsch technique ranged
from 0.78–1.15 ppb and 0.13–0.43 ppb, respectively. Possible reasons
for the discrepancy have been investigated and are discussed, however, no
satisfactory explanation has yet been found. In a subsequent laboratory
intercomparison the two techniques were in good agreement.
The observed concentrations have been compared with previous formaldehyde
measurements in the North Atlantic marine boundary layer and with other
measurements from the NAMBLEX campaign. The measurements from the Hantzsch
technique and the GC results lie at the lower and upper ends respectively of
previous measurements. In contrast to some previous measurements, both
techniques show distinct diurnal profiles with day maxima and with an
amplitude of approximately 0.15 ppb. Strong correlations were observed with
ethanal concentrations measured during NAMBLEX and the ratio of ethanal to
formaldehyde determined by the gas chromatographic technique is in good
agreement with previous measurements.
Some simple box modelling has been undertaken to investigate possible
sources of formaldehyde. Such models are not able to predict absolute
formaldehyde concentrations as they do not include transport processes, but
the results show that oxygenated VOCs such as ethanal and methanol are very
significant sources of formaldehyde in the air masses reaching Mace Head.
Citation: Still, T. J., Al-Haider, S., Seakins, P. W., Sommariva, R., Stanton, J. C., Mills, G., and Penkett, S. A.: 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, Atmos. Chem. Phys., 6, 2711-2726, doi:10.5194/acp-6-2711-2006, 2006.