A Verification of a New Coastal Area Dispersion Model

Abstract

Theoretical and experimental research of internal boundary layers (IBLs) have received much attention during the last two decades. A typical and most interesting situation involving the IBL takes place when a daytime onshore wind (sea breeze) is coupled with a significant land-sea temperature difference. In this case an intensive thermal convection within the surface atmospheric layer leads to the intensification of the turbulent mixing of air pollution. In case of a tall smoke stack close to a shoreline, pollution are at first released into a stable or neutral stratified onshore air flow. After the plume penetration into the surface mixing layer, also called the thermal internal boundary layer (TIBL), the pollutant plume is rapidly dissipated (fumigation effect); this results in high ground-level pollutant concentrations, often exceeding the accepted air quality standards. The growing tendency to locate new industrial units in coastal areas associated with increase of population densities has stimulated a great practical interest in TIBL research. Starting with the Lyons and Cole’s (1973) model, a simple scheme (Figure 1) is used to describe the TIBL phenomena as a convective ground-based underlayer with depth, H, that increases with fetch, x, from the shoreline and is defined by the following expression H = Axb where A is an empirical constant or an analytical expression containing different physical parameters such as wind speed, land-sea temperature difference or sensible heat flux, the lapse rate over a sea. Exponent, b, is usually an empirical constant of the order of 0.5 (Stander and Sethu Raman, 1985; Gryning and Batchvarova, 1990; Melas and Kambezidis, 1992 etc.). In particular, the U. S. EPA recommended Shoreline Diffusion Model (1988) bases on the above simple TIBL conception and Weisman’s formula (Weisman, 1976) for the TIBL depth. Pollution diffusion is described by the Gaussian function above the TIBL and instantly and uniformly mixed down to the ground after penetration into the TIBL.