Many inorganic and organic gaseous and aerosol products are formed in the atmosphere from atmospheric photochemical reactions. The mechanisms of formation, types of products identified, smog chamber studies, and ambient air concentrations and distributions are considered in this review. Because ozone is a key product which is widely measured, it is of considerable interest to determine whether the atmospheric distributions of other products are strongly related to that of ozone. The same products predicted by laboratory studies are present in significant concentrations in the atmosphere. The substantial ambient air concentration levels of combinations of other products is of possible concern from the air quality viewpoint. The ambient air measurement results indicate that ozone cannot be expected to serve as an adequate surrogate for the other products. The laboratory studies relating the yields of ozone and other products to initial hydrocarbon and nitrogen oxide concentration and hydrocarbon composition also indicate that the variations in other products do not closely match those of ozone.