Turbulent_diffusion

Lagrangian Gaussian puff horizontal dispersion model based on turbulent velocity fluctuation standard deviations (σu). Integrates the growth of horizontal dispersion standard deviations sigma_x and sigma_y from the Kolmogorov-type closure d(sigma)/dt = sqrt(2)*sigma_u, and computes the ground-level centerline concentration per unit mass assuming a top-hat vertical distribution within the lowest grid layer (height dz). Migrated from EnvironmentalTransport.jl@a48559c4 src/GaussianDispersion.jl:378 (GaussianKC @component). When coupled, sigma_u_x and sigma_u_y are provided by BoundaryLayerMixingKC and z_agl is provided by Puff; in standalone mode all three are treated as constant parameters.