Atmospheric diffusion equation parameters

The advantage of the deposition velocity representation is that all the complexities of the dry deposition process are bundled in a single parameter, vd. The disadvantage is that, because vd contains a variety of physical and chemical processes, it may be difficult to specify properly. The flux F is assumed to be constant up to the reference height at which C is specified. Equation (19.1) can be readily adapted in atmospheric models to account for dry deposition and is usually incorporated as a surface boundary condition to the atmospheric diffusion equation. 

The advantage of introducing the deposition velocity is to avoid a microphysical treatment of vertical diffusion and surface interfacial processes in a single mass transfer coefficient, which is measurable. The limiting application of Eq. (4.309) is because of the dependence of Vj from various parameters and states of the atmosphere and the earth s surface. Besides Eq. (4.309), the general diffusion equation is valid ... 

Assuming that these conditions are met and that the eddy diffusivities Kh and Kv are specified as functions of space and time. Equation (7) provides adequate representation of mean concentrations. Because the diffusivities are essentially empirical parameters to be determined from experimental data, the accuracy of (7) depends upon the degree to which atmospheric conditions at a location of interest correspond to the conditions under which the diffusivities were measured. 

Empirical parameters governing atmospheric dispersal pervade the literature on this subject. Like most cases of turbulent transport, elimination of a disposable coefficient in one place leads to a reappearance of one somewhere else. The present work uses an experimentally determined turbulent diffusion coefficient, D, in Equation 19. Near the ground and near the inversion base we must assign a height (z) dependence to the diffusion coefficient. 

Constituent 1 is usually assumed to be molecular hydrogen. Constituent 2 is taken to be a multicomponent noble gas mixture—excluding He, which is only weakly bound in terrestrial planet atmospheres and escapes readily by other processes. The diffusion parameter b in Equation (3), and thus the crossover mass me, differs for different elements S in constituent 2. If mc(S) is known (or assumed) for one element, say Xe, then Equation (3) for both Xe and S yields... 

The development of the computer code RALOC at the German GRS for the simulation of the distribution of hydrogen, air, and steam in a LWR containment after severe accidents has started in 1974. RALOC is based on a lumped parameter approach with a differential equation system which describes the composition of the containment atmosphere, temperature, and the transport phenomena of convection and diffusion. Validation... 

Example 5.1-2 Comparing two estimates of gas diffusion Use the Chapman-Enskog theory and the empirical correlation in Equation 5.1-9 to estimate the diffusion of hydrogen in nitrogen at 21 °C and 2 atmospheres. The experimental value is 0.38 cm /sec. Solution For the Chapman-Enskog theory, the key parameters are... 

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