Dept. of Environmental Science
Oregon Graduate Center
The measurement of the ocean-air flux of trace gases is important to understand their global budgets since the ocean can act as a source, reservoir, or sink of atmospheric gases. Many topics on ocean-air exchange are discussed in this dissertation, but the objectives were to evaluate the two-film model in its application to ocean-air exchange problems, develop a measurement protocol for carbonyl sulfide (OCS) in air and water samples, and apply the two-film model to calculate the ocean flux for OCS, CH3I, CHCl3, CH3CCl3, F-11 (CFCl3), F-l2 (CF2Cl2), CCl4, and PCE (CCl2=CCl2). The two-film model, which is widely used to calculate the flux of gases from the ocean, was compared to another more complicated model. But because of the large uncertainty in the experimental measurement of the transfer coefficients, the two-film model gave comparable results to the other model and was chosen for use in the flux calculations because of its simplicity. A propagation of error analysis of the two-film model showed that the major sources of uncertainty in flux results depend on the Henry's constant of the gas studied and the saturation value of the gas in the ocean. For gases produced in the ocean, the major source of uncertainty is in the transfer coefficient and the seawater concentration. For gases for which the ocean acts only as a reservoir, the major source of uncertainty is in the measurement of the Henry's constant (H). For OCS no measurements of H have been made in seawater, so an experimental procedure was developed to determine H for OCS as a function of temperature using atmospheric partial pressures of the gas. The results for H varied from 1.2 at 5Â°C to 2.7 at 25Â°C, and were about 20% higher than the distilled water measurements using the pure gas. For analysis of the seawater samples a method was developed for collecting, storing, and analyzing the samples in a single gas-tight bottle. This procedure allows the multiple analyses to be performed on each sample in the laboratory rather than taking equipment on board a ship. OCS was found to be stable in the sample bottles for storage periods of up to one month and was free of contamination for the fluorocarbons. The OCS samples were analyzed by a GC/MS technique which gave positive identification of the OCS peak and has a detection limit of about 35 pptv. The two-film model with the updated values for K[subscript cursive l] and H was used with the seawater data to calculate the OCS ocean flux and the flux of some halocarbon gases from seawater and air samples collected on oceanographic cruises in the Atlantic and Pacific Oceans. The ocean was found to be a significant source of OCS (0.8 Tg/yr), CH3I (0.2 Tg/yr), and CHCl3 (0.7 Tg/yr). The results for CH3CCl3, F-11, F-12, CCl4, and CCl2=CCl2 indicate that the uncertainty in the flux is large since the saturation is close to zero, and the ocean acts as a reservoir for these compounds, storing an amount close to equilibrium with the atmospheric concentrations.
Hoyt, Steven D., "The ocean-air exchange of carbonyl sulfide (OCS) and halocarbons" (1982). Scholar Archive. 67.