An analysis of the asymptotic behavior of cross-wind-integrated ground-level concentrations using Lagrangian stochastic simulation

This paper examines the asymptotic behavior as a function of downwind distance of ground-level cross-wind-integrated concentration (CWIC) caused by a continuous ground-level source in the atmospheric surface layer. We first present asymptotic expressions obtained from an analysis of data from Project Prairie Grass (PPG, Barad, 1958), and then derive corresponding formulae from data generated using Lagrangian stochastic (LS) model simulations. Under stable and neutral stratification, the formulae derived from PPG data agree well with that from LS simulations. Assuming that the Lagrangian stochastic model represents current understanding of dispersion, this agreement suggests that the formulations for stable and neutral conditions are credible. On the other hand, for unstable stratification, we find that while the LS model yields a “− 3/2” law, the PPG data suggest a fall-off with distance that is closer to a “ − 2” slope. At the present time, we cannot identify the reasons for this disagreement.