ABSTRACT

The tropospheric trace constituent formaldehyde, HCHO, was measured in rain and in the gas phase during the wet season at Enewetak Atoll, a remote marine site in the central equatorial Pacific. Rainwater averaged 8 ± 2 µg/kg; the gas phase averaged 0.4 ± 0.2 ppbv (0.5 µg/m³). These values, especially the rain, are among the lowest reported to date. The formaldehyde flux to the sea by rainout and washout extrapolates to 0.010 g/m²/y, The gaseous flux to the sea into the sea surface is estimated to be 0.05 g/m²/y by an air-sea exchange calculation that takes into account enhanced uptake by hydroxide-catalyzed formaldehyde hydration. The measured mixing ratio is close to the 0.18 ppbv prediction of a tropospheric chemistry model calculation. The methane oxidation chain probably is the sole formaldehyde source in the Enewetak area. The total formaldehyde flux as carbon into the ocean is ~2% of the estimated total organic carbon from rainout and washout. About 2-4% of the calculated column formaldehyde production is removed from the atmosphere by these processes.

Acknowledgements

This work was supported by National Science Foundation Grant OCE 77-12914 (SEAREX). M. Herrera acknowledges a Summer Student fellowship at WHOI. We thank the SEAREX logistics group and the Wet Season Chief Scientist, Dr. E. Atlas, for on-site cooperation, and Dr. A. M. Thompson for analytical hints and critical manuscript review. This is Woods Hole Oceanographic Institution Contribution Number 4506.