Chemical transformation processes in polluted atmospheres are described, with particular reference to the oil sands area in northeastern Alberta. The relevant atmospheric chemistry is discussed under four headings: clean air chemistry, oxidant chemistry, SO2 chemistry, and aerosol chemistry. It is concluded that high ozone concentrations and the formation of PAN-type oxidants would probably take place, especially during the summer when the ambient concentrations of naturally occurring reactive hydrocarbons from the wooded surroundings and other evaporated hydrocarbons at the site of the oil sand extraction plants might be sufficient to fuel the oxidant chemistry. Since the major polluting species in the oil sands area is expected to be SO2 the atmospheric chemistry of so is reviewed in detail. Homogeneous gas 2 phase reactions via interaction with oxidative processes is indicated to be a probable prime transformation route for the conversion of SO2 to sulphate during the summer, while aqueous phase reactions will be of importance all year round. Purely heterogeneous reaction routes are expected to be of minor importance. In reviewing the published literature, emphasis was given to recent studies, up to December, 1976, resulting in a list of 428 references. Those studies having direct relevance to the climatic and geographic conditions of northeastern Alberta are described in a separate chapter. In this regard, the effects of low winter temperatures and the large difference in the amount and spectral distribution of available sunlight between summer and winter are indicated and compared with results from a few other unrelated studies which can be extrapolated to northeastern Alberta, in order to make a prognosis on how these factors might influence the chemical evolution of polluted atmospheres. Atmospheric chemical transformation processes for which mechanistic or experimental data are lacking, are identified and some research projects which would lead to a better understanding and prediction of the chemistry of polluted air are outlined, with special emphasis on the particular problems which may arise in the vicinity of the oil sand extraction plants.