光化学スモッグの動特性とその制御指針

抄録

Some digital simulation studies of photochemical smog dynamics are undertaken by use of a model in which the mass transfer and the chemical reaction kinetics are described by the travelling air parcel model and by the Eschenroeder-Martinez model, respectively. Of various factors governing the formation of photochemical smog, uncontrollable factors such as meteorological and geographical conditions are fixed at some standard values while the initial concentrations of nitrogen oxides (NO_x) and hydrocarbons (HC) at the base of the air parcel are chosen as controllable factors. One daytime simulation from 7.00 to 17.00 is repeated for various sets of initial concentrations and the maximal value of the generated ozone concentration [O₃]_max and the corresponding time t_max are determined. Then, contour curves of [O₃]_max and t_max are traced on a plane whose coordinate axes correspond to the fictitious initial concentrations of NO_x and HC which will be attained if they diffuse uniformly within the air parcel.
Distinctive features of photochemical smog dynamics which are clarified through the above simulation studies suggest some useful strategies for the smog control. The generated secondary pollutant concentration depends much more on the primary pollutant composition than on its total concentration. In consequence, the suppression of total primary pollutant emission does not always result in the secondary pollutant concentration decrease, but it is much more effective to bias the primary pollutant composition toward either one of NO_x and HC in order to decrease the secondary pollutant concentration. The automobile traffic control will cause the change in the average engine operating mode together with suppression of total primary pollutant emission and so a marked change in the primary pollutant composition will result in. Therefore, an insufficient traffic control will be apt to be the cause of a secondary pollutant concentration increase.