Abstract Two 1100 ft 3 environmental chambers were utilized for the irradiation of low concentrations of auto exhaust under static conditions. The chambers were constructed of glass panels with aluminum frames. Artificial lights were used. Eye irritation was determined by human panels at various times during the irradiations. Two irritation maxima occurred during a static test. The first peak has not been correlated with any functions of the reactants or products. However, the second eye irritation peak is shown in this paper to be related to several entities, among which is the NO x defect.