The role of hydrocarbon (hc) and nitrogen oxides (nox) in photochemical smog formation was investigated. Samples of automobile exhaust with varying hc and nox levels were irradiated in a smog chamber under conditions that resulted in levels of smog manifestations similar to those observed in the atmosphere. Hc levels ranged from 0.3 to 5.0 Ppm c, and nox levels ranged from 0.08 to 1.4 Ppm. Photooxidation of nitric oxide (no) and formations of oxidant, peroxyacyl nitrate (pan), formaldehyde (hcho), and nitrogen dioxide (NO2) were used as smog manifestations. Results showed that except for the NO2 yield, all smog manifestations were intensified by increasing hc; nox inhibited the oxidant, pan, and hcho yields but promoted the rate of no oxidation and the NO2 yield. By use of these data, it was estimated that to achieve an air quality equivalent to the current California standards for oxidant and NO2, nox should be less than 0.33 Ppm and hc less than 2.5 X (nox).
Environmental Sci. and Technol., V. 6, No. 3, March 1972, PP. 253- 260