Interconversion of Primary Air Pollutants to Secondary Air Pollutants, Along with Their Removals through Delayed Mechanisms

摘要

In this paper, two - dimensional time dependent mathematical models are presented to study the fate of primary and secondary air pollutants in the atmosphere, under the variable wind speed and eddy diffusivity. Primary pollutants are emitted from an elevated line source whereas secondary pollutants are formed by chemical reactions of primary pollutants with other constituents of air The conversion of primary to secondary pollutants is considered to be the first order instantaneous process. Besides this conversion, their removals through rainout/washout are also taken to be first order process, but, instead of instantaneous, it is taken to be delayed (slow) type. The dry deposition of pollutants at the ground and leakage in the atmosphere at the inversion layer are also considered. The developed models are applied to study the conversion of sulphur dioxide to sulphate, taking place in the urban atmosphere. The numerical solutions to the models are obtained by the fractional step method in which theadvection parts are solved by the Lagrangian approach whereas for the diffusion parts, the Eulerian finite difference scheme is employed. The solutions are analysed by means of concentration profiles in order to determine the behaviour of primary and secondary pollutants with time, wind, transformation and removal processes. It is also revealed that, most of the time, the delay in removal by rainout/washout leads to lesser reduction of primary and secondary pollutants from the atmosphere as compared tono - delay.