COMPARATIVE STUDIES ON AIR POLLUTION MODELS

Abstract

Air pollution is one of those phenomena which affect both living and non-living forms on earth in a prominent manner. The earth as a whole is enclosed in a continuous air envelope and therefore any changes in it at a particular place cannot remain localised. It is. imperative to quantize the ill- effects of human or natural activities on the atmosphere and to suggest appropriate remedial measures. Air pollution or dispersion can be predicted with reasonable accuracy through different models. These have their respective weak and strong points arising out of the assumptions made therein, extent of simplifications done in solving the diffusion equation, method of estimation of diffusivity parameters, range of parameters under which these models have been tested in real life situation,etc. The present work has been planned to figure out the relative applicability of these models over a range of parameters prevailing in Indian conditions. In the present work, three basic models of air dispersion, viz., Gaussian, Pasqill-Gifford and Sutton Models have been taken. These have been tested against the experimental data obtained from a typical coal-fired boiler in a sugar mill, releasing about 40 g/s S02. The wind rose data for three consecutive months of January, February and March, 1992 have been taken for comparison. A non-reacting and non-depositing system has been assumed. Algorithms and associated mathematical correlations for computational purposes have been developed for efficient programing. FORTRAN 77 codes have been developed for all the three models and run on an IBM 486-66 MHz machine. The 3D-concentration profiles and 2D-concentration contours for a circular area having a diameter of 21 km around the stack have been plotted to show vividly the change of concentration around it with distance, wind speed and height from the ground level. The effect of timing in the 24-hour day on the ambient atmospheric conditions and hence the pollutant concentrations has also been studied. For this purpose, the 24-hour long day has been divided into morning, daytime, evening and night-time.The results of the said models have been discussed on the basis of inherent mechanisms adopted for the development of the models. The results show clearly the high concentration zones, pockets and sharp concentration profiles which vary with the time, wind direction and speed. From the above results, the latent strong and weak points of the models and their zone of applicability have been identified. The potential zones, where the monitoring units should be installed to get realistic data on pollutant dispersion, have also been located for the data under consideration.