The Numerical Analysis of the Capping Inversion Effect in a Convective Boundary Layer Flow on the Contaminant Gas Dispersion

Contaminant gas dispersion is of great concern to public health and social security. In the atmosphere, heating and cooling within a boundary layer due to the daily solar cycle result in a temperature differences, which introduces buoyancy forcing. Especially, a convective boundary layer (CBL) capped by a temperature inversion is one of the common cases in the atmospheric boundary layers during daytime conditions. Wind tunnel experimental studies have focused on the characteristics of plume dispersion under a certain thermal condition in a CBL flow. However, CBL flows have shear- and/or buoyancy-driven flows depending on atmospheric stability conditions and the influence of CBLs on plume dispersion behaviours has not been fully discussed. In this study, we performed numerical simulations of CBL flows capped by a temperature inversion with a wide range of atmospheric stability conditions and categorized distribution patterns of plume concentrations. It is found that the critical value of u*/w* in which the patterns of plume dispersion are different is around 0.4.