Atmosphere, free of trace species

2 Reactive oxygen species I OH, HO2 and H2O2 species) 5.3.2.1 Atmosphere, free of trace species 

We now extend the chemical system from pure oxygen by adding first H2O as the second abundant oxygen species in the air and learn the formation of reactive species (Table 5.6). Besides reaction (5.15), 0( D) reacts in another channel (to about 10%) with H2O to hydroxyl radicals (OH) ks.2 = 2.2 10 cule s at 298 K  

The OH radical is the most important species in the atmosphere. This is often referred to as the detergent of the troposphere because it reacts with many pollutants, often acting as the first step in their removal. Since OH (this is the neutral form of the hydroxyl ion OH , i. e. OH is an extremely weak acid) is from H2O, it returns to water by the abstraction of H from nearly all hydrocarbons RH this pathway is the definitive sink for OH. However, the organic radical R combines with O2 (reaction 5.4) and in many subsequent reactions produces organic oxygen radicals and recycles HO2 (Chapter 5.3.2.2)  

A second important pathway is the addition of OH on different species (SO2, NO, NO2) producing 0x0 acids  

A third pathway is OH transformation into the hydroperoxo radical HO2  

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