Hydroxyl radical atmospheric detergent

Most of the photo-initiated processes in the atmosphere are radical reactions. However, the hydroxyl radical ( OH) is of special significance for the chemistry of the atmosphere (Ehhalt, 1999). This reactive species is mainly responsible for the photooxidation of trace organic chemicals in the troposphere and hence for the oxidative cleansing of the atmosphere (Fabian, 1989). It is nature s atmospheric detergent (Comes, 1994, Ravishankara, et al. 1998). Furthermore, several years ago it was well established that the interaction of UV/VIS radiation and environmental pollution seems to be responsible for the dramatic forest decline that has been observed, for example in the higher areas of the Black Forest or the Ore Mountains in Germany (Schenck, 1985). 

The hydroxyl radical (OH) plays an important role in atmospheric chemistry. It is highly reactive and has a tendency to combine with a H atom from other compounds, causing them to break up. Thus OH is sometimes called a detergent radical because it helps to clean up the atmosphere, (a) Write the Lewis structure for the radical, (b) Refer to Table 9.4 and explain why the radical has a high affinity for H atoms, (c) Estimate the enthalpy change for the following reaction ... 

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) ... 

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