Air/sea gas exchange is an important component in the biogeochemical cycles of many trace gases. Eddy correlation is a direct flux measurement technique that has not been widely used for air/sea exchange due to a lack of chemical sensors with sufficient sensitivity and temporal resolution. Atmospheric pressure chemical ionization mass spectrometry (API-CIMS) is a sensitive analytical method which has the potential to measure fluxes by eddy correlation. In this research, field measurements of air/sea flux and concentration gradients of dimethyl sulfide (DMS) and acetone were made using API-CIMS in the equatorial and North Pacific Ocean.

The cruise was from May-July 2004 from Guam to Oregon. The flux of DMS (0.43-6.60 micromol m^-2 d^-1) was always out of the ocean and was correlated to both the surface seawater DMS concentrations and horizontal wind speed. Surface ocean DMS concentrations were higher in regions with higher chlorophyll content, such as the equatorial upwelling region and across the polar front. The gas exchange coefficient derived from the measurements increased with horizontal wind speed, but the functionality of this dependence is not well constrained. The gas transfer coefficients were mostly in the range between the Wanninkhof (1992) and Liss and Merlivat (1986) parameterizations.

Previous studies suggested that the ocean may be a source of acetone to the atmosphere. In this study, the acetone air/sea concentration gradient also implied that the ocean should be a source to the atmosphere in the equatorial Pacific Ocean. However, the measured acetone fluxes (1.3-16.1 micromol m^-2 d^-1) were always into the ocean and were correlated with the atmospheric acetone concentration. A global acetone ocean sink of 62 Tg yr^-1 was estimated from this data. These results suggest that the ocean is a major sink for atmospheric acetone, about half of the total global budget. The discrepancy between the acetone concentration gradient and the acetone flux suggests near surface gradients, indicating the need to investigate the surface ocean acetone budget.