Wet and dry removal of tropospheric formaldehyde at a coastal site

Abstract

Formaldehyde in precipitation and in surface seawater has been measured at Woods Hole, Massachusetts (U.S.A.) a mid-latitude coastal site. From these measurements and a calculation of the diffusion-controlled air-to-sea transfer rate of the compound we estimate the wet and dry flux of H₂CO from the troposphere to nearby coastal waters to be 6.3 μg cm⁻² yr⁻¹ for precipitation and 5.7 μg cm⁻² yr⁻¹ for gaseous diffusion. A comparison of these values with a simple photochemical model shows that these transfers may represent a significant removal mechanism for tropospheric formaldehyde. The total flux of H₂CO is equivalent to an input of 4.8 μg cm⁻² yr⁻¹ organic carbon, ≥1% of estimated total organic carbon air-to-sea transfer. The absence of a detectable amount of formaldehyde in surface seawater suggests that its fate might be biological uptake. This view is supported by the finding that seawater enriched with formaldehyde shows a gradual loss of the compound, whereas the level remains unchanged in sterile seawater under light and dark conditions.