The Inhibition of Photochemical Smog I. Inhibition by Phenol,Benzaldehyde, and Aniline

In urban atmospheres hydrocarbons promote the conversion of NO to NO₂ under the influence of sunlight, ultimately giving rise to photochemical smog. The conversion results from a long chain process with HO radicals as the chain carrier. If this chain could be interrupted by suitable radical traps, the formation of photochemical smog would be inhibited. In this paper we report the results of studies using phenol, benzaldehyde, and aniline as inhibitors. Mixtures containing 16 mTorr C₃H₆, 8 mTorr NO, ～85 Torr 0₂, and the addi tives were irradiated at 25°C. The NO₂ pressure was monitored photometrically. In the absence of additive, the NO2 pressure first increases with irradiation time reaching a maximum conversion corresponding to 70% of the NO at 1 2 minutes. As the radiation time is lengthened, the NO₂ pressure drops. With the additive present, the formation of NO₂ is delayed. The time to reach the maximum percent conversion of NO to N0₂ becomes 20, 22, 31, and 40 minutes respectively, for 13 mTorr C₆H₅OH, 2 mTorr C₆H₅CHO, 8 mTorr C₆H₅CHO, and 4.1 mTorr C₆H₅NH₂ added. The problems and possibilities of adding inhibitors to the atmosphere to control air pollution are discussed.