Air-sea exchange

The magnitude and direction of the net flux, f, of any gaseous species across an air-water interface. 

The parameters and ki are the transfer velocities for chemically unreactive gases through the viscous sublayers in the air and water, respectively. They relate the flux F to the concentration gradients across the viscous sublayers through expressions similar to equation (40)  

The parameter a in equation (41) quantifies any enhancement in the value of fci due to chemical reactivity of the gas in the water. Its value is unity for an uru-eactive gas for gases with rapid aqueous phase reactions (e.g. SOj), much higher values can occur. 

A comparison of the resistance in air and water for different gases shows that the resistance in the water dominates for gases with low solubility that are unreactive in the aqueous phase (e.g. O2, N2, CO2, CH4). For gases of high solubility or rapid aqueous chemistry (e.g. H2O, SO2, NH3), processes in the air control the interfacial transfer. 

The numerical values of the transfer velocity K for the different gases are not well established. Its magnitude depends on such factors as wind speed, surface waves, bubbles, and heat transfer. A globally averaged value of K often used for CO2 is about 10 cm/h. Transport at the sea-air interface is also discussed in Chapter 9 (for a review, see Liss, 1983). 

The oceans cover some two-thirds of the Earth s surface and consequently provide a massive area for exchange of energy (climatologically important) and matter (an important component of geochemical cycles). 

Airborne concentrations of particulate pollutants are not uniform over the sea. The spatial distribution of zinc over the North Sea  

As explained in Chapter 4, the sea may be both a source and a sink of trace gases. The direction of flux is dependent upon the relative concentration in air and seawater. If the concentration in air is Ca, the equilibrium concentration in seawater, (equ) is given by 

In addition to dry deposition, trace gases and particles are also removed from the atmosphere by rainfall and other forms of precipitation (snow, hail, etc.), entering land and seas as a consequence. Wet deposition may be simply described in two ways. First, 

Typical values of scavenging ratio lie within the range 300-2000. Scavenging ratios are rather variable, dependent upon the ehemieal nature of the trace substance (particle or gas, soluble or insoluble, etc) and the type of atmospheric precipitation. Incorporation of gases and particles into rain can occur both by in-cloud scavenging (also termed rainout) and below-cloud scavenging (termed washout). 

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Climate Change and Air-Sea Exchange of CO2. The air-sea exchange flux of CO2 is governed by the gas exchange rate and by the difference between... 

Andreae, M. O. (1986). The ocean as a source of atmospheric sulfur compounds. In "The Role of Air-Sea Exchange in Geochemical Cycling" (P. Buat-Menard, ed.). Reidel, Dordrecht. 

Dissociation of the neutral acid in water necessitates modifications for air-sea exchange in the model, which is based on Henry s law. Other possible pathways, e.g. sea spray, are neglected. Henry s law is restricted to concentrations of physically solved, non dissociated substances. Since only the non-dissociated acid is volatile, it is important to correct the air-water partition coefficient as to reflect the relative proportions of volatile and non-volatile components. The corrected parameter is the effective Henry s law coefficient, which is related to the Henry s law coefficient as a function of pH (modified Henderson-Hasselbalch equation) ... 

Ho et al (2004) showed for SF6 that in low wind conditions short intense rain events accelerate gas exchange in the marine environment. Extending air-sea exchange by including this process is also of interest in the context of climate change, as climate projections suggest that the intensity of rain events will increase [Roeckner et al (2006)]. 

Zhou, X., Mopper, K. (1990) Apparent partition coefficients of 15 carbonyl compounds between air and seawater and between air and freshwater Implications for air-sea exchange. Environ. Sci. Technol. 24, 1864-1869. 

Lerman, A. Mackenzie, F.T. 2005. 0O2 air-sea exchange due to calcium carbonate and organic matter storage, and its implications for the global carbon cycle. Aquatic Geochemistry, 11, 345-390. 

Air-sea exchange rates of gases that directly influence global ecosystems. 

Lynch-Stieglitz, J., T.F. Stocker, W.S. Broecker, and R.G. Fairbanks. 1995. The influence of air-sea exchange on (Delta)C-13 of (Sigma)C02 in the surface ocean Observations and modeling. Global Biogeochemical Cycles 9(4) 653-665. 

Atlas, E., Foster, R., and Giam, C.S. Air-sea exchange of high molecular weight organic pollutants laboratory studies, Environ. Sci Technol, 16(5) 283-286, 1982. 

Hunter-Smith, R.J., Balls, P.W., andLiss, P.S. Henry slaw constants and the air-sea exchange of various low molecular weight halocarbon gases, Tellus, 35B(3) 170-176, 1983. 

Liss, P. S., and L. Merlivat, Eds., Air-Sea Gas Exchange Rates Introduction and Sythesis, The Role of Air-sea Exchange in Geochemical Cycling, D. Reidel Publishing, Dordrecht, The Netherlands, 1986. 

Liss PS, Merlivat L (1986) In Baut-Menard P (ed) The Role of Air-Sea Exchange in Geochemical Cycling. Reidel Publishing Co, Dordrecht, Holland p 113... 

Slinn WGN (1983) In Liss PS, Slinn WGN (eds) Air-Sea Exchange of Gases and Particles. Reidel, Dordrecht, The Netherlands p 299... 

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