SINGLET OXYGEN IN ENVIRONMENTAL SCIENCES SINGLET MOLECULAR OXYGEN AND PHOTOCHEMICAL AIR POLLUTION

Singlet molecular oxygen (O2) may play a significant role as an oxidant in photochemical air polution. Reaction of electronically excited oxygen with olefinic substances produces thermally unstable hydroperoxides which may be involved in the rapid conversion of NO into NO2, a process not well understood in photochemical air pollution. Several mechanisms for the formation of 1O2 are examined critically in relation to their possible importance in the chemistry of urban atmospheres. In each, the excitation energy is derived ultimately from the sun's radiation, but the energy may be utilized by direct absorption of radiation by ground state 3O2, by photolysis of an atmospheric contaminant to form excited 1O2 in the primary step, by spin-conserved energy transfer mechanism in which an atmospheric contaminant absorbs solar radiation and transfers its excitation to ground state 3O2, or by exothermic chemical reactions involving atmospheric contaminants which themselves originated in a photochemical process. © 1969, American Chemical Society. All rights reserved.