Ozone free radical species generation

As introduced in 17.1.2.3, solvents may be photodegraded in both water and air. Atmospheric chemical reactions have been studied in detail, particularly in the context of smog formation, ozone depletion, and acid rain. The absorption of light by chemical species generates free radicals which are atoms, or groups of atoms that have unpaired electrons. These free radicals are very reactive, and can degrade atmospheric solvents. Atmospheric ozone, which occurs in trace amounts in both the troposphere (sea level to about 11 km) and in the stratosphere (11 km to 50 km elevation), can degrade solvents. Ozone is produced by the photochemical reaction ... 

The gas phase oxidation of sulphur dioxide has probably been studied in more detail than any other atmospheric species. In general terms the types of reaction are also appropriate to NO They involve the oxidation of sulphur dioxide and NO by free radicals - namely the hydroxyl radical generated by the photolysis of ozone - to form an acid aerosol. In polluted atmospheres where there are larger quantities of NO and hydrocarbons generating photo-oxidants/ there is evidence to suggest that the aerosols formed will be a mixture of sulphuric and nitric acids. In other words/ the conversion process to sulphates and nitrates will take place much more readily when the acid pollutants emitted pass through polluted air (more likely to be over land/ than over water). 

The essential oxidation rate steps in the environment involve reactive species such as free radicals (RO2RO, HO ), ozone, and 02 (singlet oxygen). For predictive purposes, it is important to identify the important oxidants and their concentrations in the environmental compartments. Values of many oxidation rate constants are known reliably (Hendry etal, 1974). In the atmosphere, oxidation by the OH radical is significant, whereas ozone is important in the oxidation of some olefins and possibly some sulfur or phosphorus compounds. The RO2 radical can be important in sunlight photolysis in natural waters. Competitive kinetic techniques could be used to evaluate the relative loss of two chemicals, one of which is a standard of known reactivity to a specific oxidant (Mill etal., 1978). Azo compounds could be used to generate RO2 radical in water, nitrous acid to form the HO radical in air, and a dye to generate 02 in water. 

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