Hydroxyl radical gaseous phase

In a gaseous phase enriched with water vapor, the mechanism of photolysis involves the release of a molecule of oxygen and an atom of oxygen (1D). The latter may react with water to produce hydroxyl radicals ... 

In contrast to the water phase the HO radicals can have a much longer lifetime in gaseous media, i.e. up to 1 s for the OH and 60 s for the HO radical, respectively (Fabian, 1989). Despite the low concentration of OH radicals of about 10 molecules per cm in the sunlit troposphere (Ehhalt, 1999) they play an important role in controlling the removal of many organic natural and manmade compounds from the atmosphere (Eisele et al., 1997, Eisele and Bradshaw, 1993). Even in indoor environments, the formation of hydroxyl radicals is possible by ozone/alkene reactions (Atkinson et al., 1995). Steady-state indoor hydroxyl radical concentrations of about 6.7x10 ppb equivalent to 1.7x10 molecules cm were calculated at an ozone concentration of 20 ppb (Weschler and Shields, 1996). 

It has been shown recently that a hydroxyl radical may partition from the gaseous to the aqueous phase, or may be formed directly in the aqueous phase, and there effect the oxidation of sulfur dioxide. Sulfur dioxide can also be oxidized inside raindrops by hydrogen peroxide, H2O2, which is a minor atmospheric species formed principally by the disproportionation of HO2 radicals... 

Table 1 Physico-chemical properties saturation vapour pressure, ps j, Henry s law constant, K, and octanol-water partitioning coefficient, K , and degradability in air as the reaction rate coefficients of the hydroxyl radical with the gaseous and the particulate phase molecules, kg oh and 1% oh> respectively, of 17 parent PAHs and 1 alkylated PAH (retene) (298 K ten Hulscher et al. 1992 Finlayson-Pitts and Pitts 2000 Perraudin et al. 2007)...

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