Vertical diffusion from elevated line sources were estimated using the structure model of the atmospheric boundary layer proposed by Yokoyama et al. (1977a, b, c). The twodimensional differential equation of diffusion was computed numerically for stationary and horizontally homogeneous conditions. Eddy diffusivity for elevated sources was assumed to be proportional to the travel time of diffusing particles in the early stage of diffusion, and in the long range, proportional to the eddy diffusivity of momentum. From this model the Lagrangian time scale of eddies in the vertical direction is estimated and compared with experiments.The estimated vertical spread normalized by characteristic parameters of turbulence at the source height can be approximated by the relation derived from Taylor's statistical theory with an exponential Lagrangian velocity correlation function.The results were compared with experiments and a simplified relation between σz/σEs (σEs: standard deviation of elevation angle at the source height) and downwind distance was proposed for practical application.
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