الفهرس Only 14 pages are availabe for public view
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Abstract
The atmosphere is an important medium for transport and transformation of pollutants.
Air pollutants can be emitted directly from sources (primary pollutants) or can be formed or transformed in the atmosphere as a result of chemical transformations (secondary pollutants). The air pollutants give rise to adverse effects on human health or transfer of toxic substances to freshwater, seawater, soil and vegetation, which can lead to acidification. In addition air emissions can lead to global effects like the green house effects and depletion of ozone in stratosphere. The air pollutants must be assessed according to their spatial and temporal distribution in order to establish efficient control strategies. The assessment and management have to be based on reliable data and knowledge about the processes involving the pollutants, i.e. often based on a combination of measurement and air quality models describing dispersion processes and chemical and physical transformations. The design of industrial complexes, community planning, identification of significant sources, and prediction of pollutant concentrations at selected receptors are usually done using mathematical models. Important inputs to air pollution models include the type, character, and distribution of the sources; the pollutants emitted; meteorological variables which determine’the transport and dispersion of pollutants.
The forced plume model described here is a gross parameter numerical model in which conservation equations are integrated over the cross-section profile and hence it is of importance to realize the full implications of different assumptions about the distribution of parametric values across the cross-section. It is assumed that quantities (both observed and predicted) are temporally averaged (over a period of several minutes i.e. long enough for small timescale random fluctuations to be smoothed out but short enough for ambient conditions to be regarded as stationary), this assumption is in accord with all previous attempts to calculate plume trajectories and ground level concentrations. Hence the model is formulated as a steady state model in which the time derivatives are set equal to zero. The proposed model is finally used to perform systematic theoretical investigation of various parameters along with their effects on plume rise and ground level concentrations of pollutant.
In the present work to control the emitted emissions from its sources some variables as stack height and stack exit temperature can be increased to make the pollutants travel long distance before reaching to the ground to achieve ground level concentration levels less than air quality standards. It can be seen also from the above mentioned discussion that some variables as stack exit velocity and stack diameter can led to the same effect but this is somewhat misleading insofar as increasing stack radius and stack exit velocity in the model effectively increases the total effluent emitted and hence cannot relate to the same source but to larger industrial sources. The other types of parameters are un-controlled parameters as ambient conditions wind speed and ambient temperature where there is no control on these parameters.