Chemical Modelling Studies of the Long-Range Dispersion of Power-Plant Plumes
A comprehensive chemical model of gas-phase plume/ambient interactions using simple dispersion terms has been developed. Simulations have been carried out for an idealised source emitting into ambient air masses with different histories with particular reference to the formation of acidic species. Diurnal and seasonal effects together with the influence of ambient air composition and plume expansion rate have been investigated for dispersion times up to 19 hours.
The model predictions indicate that in general, greater chemical conversion of plume components occurs in material emitted in the late afternoon and overnight than in material emitted in the morning, and that chemical reactions are faster in Summer than in Winter. However, the nett quantitative environmental effect of the plume is a complex function of the physical and chemical parameters which cannot be determined a priori and further modelling studies are required before universally applicable simplifications to the chemical scheme can be made.
In addition to the general studies, the model has been modified to simulate, in an idealised manner, a specific case study in which a labelled power plant plume was tracked and analysed by instrumented aircraft on a trajectory from the U.K. over the North Sea. For these experiments conducted on a clear sunny day, satisfactory agreement between measured values for the important gaseous plume constituents and model predictions are obtained.
KeywordsDeposition Velocity Order Rate Constant Nitric Acid Concentration Sulphur Acid Concentration Flight Simulation
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