Air and water are the two most important fluids on Earth. The physical processes at the surfaces of oceans, estuaries, rivers, and lakes relevant to the exchange of chemicals between the two phases are extremely complicated and variable. For relatively calm conditions, the air-surface water interface is smooth, and a mixture of theoretical concepts and empirical knowledge allows reasonable prediction of the rates of interface mass transfer.

Traditionally, water vapor is used as the test substance for determining the air phase mass-transfer coefficient, \(k_{c i a}\), for any component \(i\). The corresponding relation is (Johnson, 2010)

Here

Based on the theory of wind friction in a boundary layer, a model called the Coupled Ocean-Atmospheric Response Experiment (COARE) is used to estimate $k_{c w a}$ as follows (Johnson, 2010):

Here: \(k_{c w a}\) air phase mass-transfer coefficient for water vapor in air \((\mathrm{cm} / \mathrm{s})\) \(u_{10}\) wind speed measured \(10 \mathrm{~m}\) above the water surface \((\mathrm{m} / \mathrm{s})\)

Estimate the air phase mass-transfer coefficient for methanol when the atmospheric conditions are \(298 \mathrm{~K}, 1 \mathrm{~atm}\), and measured wind speed of \(15 \mathrm{~m} / \mathrm{s}\) at an elevation of \(10 \mathrm{~m}\). Under these conditions, the kinematic viscosity of air is \(v=0.155\) \(\mathrm{cm}^{2} / \mathrm{s}\). Use the mass diffusivities values listed in Appendix A.

Data From List of Appendix A:-

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kcia = k Scia cwa Sc... wa -2/3 (2-114)