Interfacial Mass Transport and Aqueous-Phase Reactions

3 Interfacial Mass Transport and Aqueous-Phase Reactions 

Despite the fact that for typical cloud droplets gas-phase mass transport is in the continuum regime, mass transport across the air-water interface is, ultimately, a process involving individual molecules. Therefore the kinetic theory of gases sets an upper limit to the flux of a gas to the air-water interface. This rate is given by (12.25) and depends on the value of the accommodation coefficient. 

Following our approach in Section 12.3.1 the molar flux per droplet volume through the interface, will be 

This rate reaches a maximum value for cs = 0. Converting to partial pressure,, / x, the maximum molar uptake rate through the interface will be 

FIGURE 12.8 Maximum molar uptake rate per ppb of gas-phase reagent as a function of cloud drop diameter, as controlled by gas-phase diffusion, or interfacial transport for various accommodation coefficient values at T = 298 K and for Dg = 0.1 cm2 s l and MA = 30 g mol 1 (Schwartz 1986). 

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Considering a system at steady state with only interfacial mass transport and aqueous-phase reactions taking place (the rest of the mass transport steps are assumed to be fast), then Raq = Ri, or... 

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