Numerical simulation of particle trajectories in inhomogeneous turbulence,III: Comparison of predictions with experimental data for the atmospheric surface layer

It is shown that predictions of a numerical trajectory-simulation method agree closely with the Project Prairie Grass observations of the concentrations 100 m downwind of a continuous point source of sulphur dioxide if the height (z) dependence of the Lagrangian length scale Λ _L is chosen as: whereL is the Monin-Obukhov length. The value of 0.5 for Λ _L /z in neutral conditions is consistent with the findings of Reid (1979) for the Porton experiment, and is also shown to be the best choice for simulation of an experiment in which concentration profiles were measured a short distance (< 40 m) downwind of an elevated point source of glass beads (40 μn diameter). $$begin{gathered} Lambda _L = 0.5zleft( {1 - 6frac{z}{L}} right)^{{1 mathord{left/ {vphantom {1 4}} right. kern-nulldelimiterspace} 4}} L< 0 hfill Lambda _L = 0.5z/left( {1 + 5frac{z}{L}} right)L > 0 hfill end{gathered} $$