Plume Model for Nitrogen Oxides

Abstract

A local scale dispersion plume model including atmospheric chemistry 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. coal- fired power plants. Problems concerning both high concentrations of NO2 in the air and deposition of different nitrogen compounds to the ground are considered.

In the numerical model 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 have to be included. On a somewhat larger scale the number of reactions needed increase substantially. For the numerical solution we have used the method by Gear.

Instantaneous plume concentrations and the NO₂ fraction of the total N0_x in the plume at different conditions are obtained directly from the above mentioned calculations. In order to obtain 1-h 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 condition and the ambient ozone concentration are of great importance for the ralative amount of NO₂ in the plume.