Singlet oxygen in polluted environments

Abstract

The role of singlet oxygen (O2*) in the troposphere is considered at concentrations of the order of the steady state between the sources and the sinks. The production terms evaluated include the collisionally induced absorption of solar energy, the Hartley photolysis of ozone, exothermic chemical reaction, and energy transfer from triplet states of organic molecules. The triplet states of organic molecules are shown to be a large potential source of O2(1Δg) if the quantum yield for the process approaches unity. The major sink for O2* is quenching. Recent experimental values for singlet oxygen quenching are employed to obtain steady-state concentrations of O2*. The minimum concentrations of O2(1Δg) so obtained are shown to be sufficiently high to affect the oxidation of olefins, and they may play an important role in explaining the infamous material imbalance in chamber studies if the actual concentrations are somewhat higher. The role of singlet oxygen in the conversion of NO to NO2 via the Pitts mechanism is also discussed.