Local scale plume model for nitrogen oxides. Model description.

Type: Report
Series: RMK 41
Author: Persson, C., and Funkquist, L.


A plume dispersion model on local scale ( 0 - ~ 20 km) including atmospheric chemis try for nitrogen oxides is developed. The purpose of the study is to obtain a practical air quality model which can be used in environmental planning for e.g. coalfired power plants. Problems concerning both high concentrations of NO2 in the air and deposition of different nitrogen compounds to the ground are considered. The instantaneous plume dilution is described - assuming total mixing within the plume - as a function of emission parameters and meteorological conditions. The interplay of emissions, instantaneous plume dilution, entrainment of polluted ambient air,  meteorological conditions and atmospheric chemistry processes determines the production or loss of the different compounds. On a local scale only six chemical reactions need to be included. On a somewhat larger scale the  number of reactions needed increases substantially. For the numerical solution we have used the method by Gear. In order to obtain hourly mean values of different nitrogen oxides and long- term deposition values, conventional Gaussian respectively K-formulation procedures are used. Meteorological input  data are obtained from climatological observations and also generated by a boundary layer model. From the results it is obvious that the meteorological conditions and the ambient ozone concentration are of great importance for the relative amount of NO2 in the plume. On a local geographical scale the plume chemistry is diffusion controlled.