May 1976

Document Type


Degree Name



Dept. of Environmental Technology


Oregon Graduate Center


A generalized photochemical smog mechanism is used to evaluate the photochemical smog potential due to solar radiation for different seasons and different locations in the northern hemisphere. This is done by expressing the photolytic rate constants as functions of the ground level solar flux and expressing the solar zenith angle as a function of latitude, time of year and time of day. The irradiation of a specified mixture of hydrocarbons and nitrogen oxides is simulated at local times 0900 - 1200 and 0600 - 0900. The hydrocarbon mixture is chosen to correspond approximately to that of an urban atmosphere. The differential rate equations are solved using a modified Hammings predictor-corrector method, and reasonable computing times are obtained by applying the pseudosteady state assumption to the reactive radicals. The study shows that during the summer months the potential for photochemical smog formation extends far north, well beyond 60°N. After three hours of simulated irradiation in June the ozone level at 60°N was 75-80% of that at 34°N. In the spring and fall the region in which photochemical smog may be expected narrows. At equinox the ozone concentration at 60°N was 35-40% of that at 34°N. Locations at latitudes 60°N and higher can therefore not be excluded as future problem areas with regard to photochemical smog. The concentration levels of peroxyacylnitrates and aldehydes were well correlated with the ozone levels, and so was the time required to obtain maximum concentration of nitrogen dioxide in the photochemical cycle. The magnitude of the NO2 peak was not much affected by the variations in latitude and season, and the magnitude of the NO2 peak decreased slightly when the solar flux increased.





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