Detailed gas exchange measurements from two circular and one linear wind/wave tunnels are presented. Heat, He, CH4, CO2, Kr, and Xe have been used as tracers. The experiments show the central importance of waves for the water-side transfer process. With the onset of waves the Schmidt number dependence of the transfer velocity k changes from k o• Sc-2/3 to k o• Sc-•/2 indicating a change in the boundary conditions at the surface. Moreover, energy put into the wave field by wind is transferred to near-surface turbulence enhancing gas transfer. The data show that the mean square slope of the waves is the best parameter to characterize the free wavy surface with respect to water-side transfer processes. 1. , • !• 0.010 ! ß ß ! ß ß o o ! ß , ß ß 10 o 10 • 10 z ?requemcy [Hz] across the free aqueous viscous boundary layer, Tellus, in press, 1985b. J•ihne, B, G. Heinz, and W. Dietrich, Measurements of the diffusion coefficients of sparingly soluble gases in water with a modified Barrer method, submitted to J. Geophlts. Res., 1986. Kanwisher, J., On the exchange of gases between the atmosphere and the sea, Deep Sea Res., I0, 195-207, 1963. Kitaigorodskii, S. A., On the theory of the equilibrium range in the spectrum of wind-generated gravity waves, J. Phys. Oceanogr.., 15, 816-827, 1983. Kitaigorodskii, S. A., On the fluid dynamical theory of turbulent gas transfer across an air-sea interface in the presence of breaking wind-waves, J. Phys. Oceanogr., I4, 960-972, 1984. Kondo, J., Parameterization of turbulent transport in the top meter of the ocean, J. Phys. Oceanogr., 6, 712-720, 1976. Lange, P. A., B. J•hne, J. Tschiersch, and J. Ilmberger, Comparison between an amplitude-measuring wire and a slope-measuring laser water wave gauge, Rev. Sci. Instrurn., 53, 651-655, 1982. Ledwell, J. R., Gas ezchange across the air-water interface, Ph.D. thesis, Harvard Univ., Cambridge, Mass., 1982. Ledwell, J. R., The variation of the gas transfer coefficient with molecular diffusity, in Gas 2•nsfer at Water Surfaces, edited by W. Brutsaert and G. H. Jirka, pp. 293-302, D. Reidel, Hingham, Mass., 1984. Liss, P.S., Processes of gas exchange across an air-water interface, Gas exchange dependency on diffusion coefficient: Direct 222Rn and SH• comparisons in a small lake, J. Geophlis. Res., 87, 546-556, 1982. Weit•er, F., Verdunstungsmessungen in einem ringf6rmigen Wind-Wasser-Kanal mir Hilfe yon Psychrometern und einem WLD-System, Staatsexamensarbeit, Inst. filr Umweltphys., Univ. Heidelberg, 1980. Witting, J., Effects of plane progressive irrotational waves on thermal boundary layers, J. l•uid Mech., 50, 321-334, 1971. Wu, J., Wind-induced drift currents, J. l•uid Mech., 68, 49-70, 1975.

The diffusion coefficients D of important gas tracers dissolved in water and seawater were measured with a modified Barrer method. The measurements include the gases He, Ne, Kr, Xe, H2, CH4, and CO2 dissolved in distilled water in the temperature range from $ to 35øC, and He and H• dissolved in seawater in the same temperature range. The maximum systematic error is estimated to be well below $%. The isotopic fractionation in the diffusion coefficient, eD, was determined to be (-0.87 q-0.05)%0 for •3CO•/t •CO2 and (15 q-3)% for SHe/4He.

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Abstract. Nitric oxides (NOx) play a very important role among the anthropogenic trace gases. They affect human health and have an impact on ozone chemistry and climatic change. Here we describe a new method for the quantification of the global NOx budget from image sequences of the Global Ozone Monitoring Experiment (GOME) spectrometer on board the ERS 2 satellite. In contrast to measurements using ground-based or balloon-or aircraft-borne sensors, this instrument provides, for the first time, the possibility of observing global maps of NO2 column densities. As part of this work, algorithms were developed to analyze GOME spectra numerically and to extract physically relevant parameters from the resulting maps using image-processing techniques. Column densities of NOx were determined using differential optical absorption spectroscopy (DOAS) [Platt, 1994]

▪ Abstract  The exchange of inert and sparingly soluble gases—including carbon dioxide, methane, and oxygen—between the atmosphere and oceans is controlled by a thin 20- to 200-μm-thick boundary layer at the top of the ocean. The hydrodynamics in this layer are significantly different from boundary layers at rigid walls, since the orbital motion of the waves is of the same order as the velocities in the viscous boundary layer. Laboratory and field measurements show that wind waves significantly increase the gas transfer rate and that it is significantly influenced in this way by surfactants. Because of limited experimental techniques, the mechanisms for this enhancement and the structure of the turbulence in the boundary layer at a wavy water surface are still not known. A number of new imaging techniques are described that give direct insight into the processes and promise to trigger substantial theoretical progress in the near future.

[1] The influence of wind stress, small-scale waves, and surface films on air-sea gas exchange at low to moderate wind speeds (<10 m s À1 ) is examined. Coincident observations of wind stress, heat transfer velocity, surface wave slope, and surface film enrichments were made in coastal and offshore waters south of Cape Cod, New England, in July 1997 as part of the NSF-CoOP Coastal Air-Sea Chemical Fluxes study. Gas transfer velocities have been extrapolated from aqueous heat transfer velocities derived from infrared imagery and direct covariance and bulk heat flux estimates. Gas transfer velocity is found to follow a quadratic relationship with wind speed, which accounts for $75-77% of the variance but which overpredicts transfer velocity in the presence of surface films. The dependence on wind stress as represented by the friction velocity is also nonlinear, reflecting a wave field-dependent transition between limiting transport regimes. In contrast, the dependence on mean square slope computed for the wave number range of 40-800 rad m À1 is found to be linear and in agreement with results from previous laboratory wind wave studies. The slope spectrum of the small-scale waves and the gas transfer velocity are attenuated in the presence of surface films. Observations over largescale gradients of biological productivity and dissolved organic matter show that the reduction in slope and transfer velocity are more clearly correlated with surface film enrichments than with bulk organic matter concentrations. The mean square slope parameterization explains $89-95% of the observed variance in the data and does not overpredict transfer velocities where films are present. While the specific relationships between gas transfer velocity and wind speed or mean square slope vary slightly with the choice of Schmidt number exponent used to scale the heat transfer velocities to gas transfer velocities, the correlation of heat or gas transfer velocity with mean square slope is consistently better than with wind speed.

Two‐dimensional wave slope spectra have been measured in the large Delft wind‐wave facility using an imaging optical technique and digital image processing. The data cover wavelengths from 0.4 to 24cm and wind speeds (U10) from 2.7 to 17.2 ms−1. The spectral densities of small gravity waves at higher wind speeds are proportional to k−3.5 and u*. Capillary‐gravity and capillary waves show features which clearly manifest that the energy balance for these waves is much different from that for gravity waves. The degree of saturation is approximately constant at a given wind speed, but strongly increases with friction velocity (∝ u*2.5). A sharp cutoff, which is almost independent of the wind speed, occurs at a wavelength of about 7 mm.

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