Simulação analítica da dispersão de poluentes durante o período de transição dia-noite

Abstract

In this work, an analytical Eulerian model was employed to simulate the pollutants concentration released from continuous point source during the sunset transition period. The analysis applies the dispersion model parameterized by the stable and decaying convective eddy diffusivities, representing the turbulent mixing in the stable boundary layer and pre-residual layer. The concentration simulations were calculated considering different times in the transition process through the sunset period and CLE height of 60m and 120m. The results presented In this work show similarity with ones reported by literature, where the mixing strong action caused by the decaying convective energy-containing eddies in the pre-residual layer causes an effective entrance of pollutants to the interior of the recently established SBL. Analyzing the concentrations for a height of 60m , we have to during the initial stage of the transition period, in which the SBL presents a small depth, the combination between residual convective and stable eddies acts efficiently to transport the pollutants in direction to the ground surface. For the later stages, the height of the SBL depth reaches the point source height so that the dispersion occurs in a large vertical extension that is dominated by a stable turbulence. For CLE height of 120m, happen same behavior for height of 60m, for the after phases there is not surface decrease concentration according as occurs the loss convective diffusion capacity inside pre-residual layer and the CLE height increase. The lack of an effective turbulent mixing, acting over the vertical extension of the SBL, prevents that pollutants do reach the surface. In the present contribution was focused on an analytical description of the pollutant dispersion occurring around the evening transition, which allows simulate the turbulent transport in a computationally efficient procedure.