SMOG CHAMBER STUDIES OF TEMPERATURE EFFECTS IN PHOTO-CHEMICAL SMOG

Irradiations of selected hydrocarbon-NOx-air mixtures were carried out over the temperature range -3 to 60 °C in a 5800-L, thermostated evacuable environmental chamber. The federal air quality standard for ozone, 0.08 ppm (1-h average), was exceeded within 6 h of irradiation of a surrogate hydrocarbon-NOx mixture approximating an urban atmosphere, even at 5 °C. In all three systems studied (propene, toluene, and surrogate), rates of ozone formation increased significantly with temperature. In propene-NOx-air and in tolu-ene-NOx-air reaction mixtures, the amounts of hydrocarbon consumed and the approximate amounts of NO to NO2 conversion increased significantly with temperature. The nature of the O3 concentration-time profiles in high concentration propene-NOx experiments was significantly affected by temperature. In runs between 11 and 33 °C, [O3] peaked slightly before most of the initially present NOx was consumed as is usually the case. However, for T ≤ 11 °C, [O3] peaked significantly earlier and, for T ≥ 33 °C, significantly later than the time of NOx consumption. Furthermore, in a run at T ≃ 50 °C, [O3] reached a maximum prior to complete NOx consumption, then decreased slightly, and finally slowly increased to a second maximum. The mechanistic implications of these observations are discussed. © 1979, American Chemical Society. All rights reserved.