UNSTEADY STATE DISPERSION OF AIR POLLUTANTS UNDER THE EFFECTS OF DELAYED AND NONDELAYED REMOVAL MECHANISMS

Abstract In this paper, we present a two‐dimensional time‐dependent mathematical model for studying the unsteady state dispersion of air pollutants emitted from an elevated line source in the atmosphere under the simultaneous effects of delayed (slow) and nondelayed (instantaneous) removal mechanisms. The wind speed and coefficient of diffusion are taken as functions of the vertical height above the ground. The deposition of pollutants on the absorptive ground and leakage into the atmosphere at the inversion layer are also included in the model by applying appropriate boundary conditions. The model is solved numerically by the fractional step method. The Lagrangian approach is used to solve the advection part, whereas the Eulerian finite difference scheme is applied to solve the part with the diffusion and removal processes. The solutions are analyzed to observe the effects of coexisting delayed and nondelayed removal mechanisms on overall dispersion. Comparison of delayed and nondelayed removal processes of equal capacity shows that the latter (nondelayed) process is more effective than the former (delayed removal) in the removal of pollutants from the atmosphere.     

MODELING THE EFFECTS OF URBAN HEAT ISLANDS GENERATED MESOSCALE WIND ON AIR POLLUTION DISPERSION IN A PATCHY ATMOSPHERE

Abstract The paper presents a steady‐state two‐dimensional mathematical model to study the dispersion of air pollutants continuously emitting from a point source in a patchy atmosphere. The first patch, which extends to some downwind distance from the source (present in first patch), is the urban center, whereas the second patch is its adjacent countryside. For simulating the effects of urban heat islands on pollutant distribution, a local mesoscale wind is introduced in the first patch along with the usual large‐scale wind. Keeping in mind the real‐life situations, the meteorological, deposition, and removal parameters are taken to be different in different patches. The concentration of pollutants in both the patches has been computed under different stability conditions of the atmosphere through finite difference scheme. The results of the model show that the urban heat island (mesoscale wind) has a tremendous impact on air pollution distribution, both over the urban center as well as its adjacent countryside (rural). The model solutions also reveal about the concentration distribution of pollutants in different parts of the atmosphere in different atmospheric conditions.