Numerical investigation of meso- and microscale diffusion of Tbilisi dust

Abstract

Meso- and micro-scale processes of dust propagation in the atmosphere of the city of Tbilisi and its surrounding territory are modelled using 3D regional model of atmospheric processes and an admixture transfer-diffusion equation. Terrain-following coordinate system is used with the purpose of taking into account the impact of very complicated relief on the atmosphere pollution process. It is obtained via modelling that meso-scale propagation of the dust substantially depends on relief form of surrounding territory, background wind speed and its direction. In the second half of the day the mountain-and valley circulation process due to Tbilisi region relief in condi- tions of background light air causes a change of dust transfer direction in the lower 100m surface layer. The dust dissipated from Tbilisi city in the atmosphere is basically concentrated in lower 600 m of the boundary layer and it is propagated in the narrow zone with length about more than 80 km and width 20-24 km. Modelling of dust micro-scale diffusion process in Tbilisi city shows that the maximum concentrations 1.5-2.0 MAC are obtained from 3.00 p.m.to 9.00 p.m. in vicinity of central avenues and in the southern part of the city. The spatial dust distribution in the lower part of the atmospheric surface layer depends on vehicle traffic intensity, as well as on spatial distribution of highways, and micro-orography of the city and surrounding territories.