Chapman reactions

Oxygen atoms produced by the ultraviolet dissociation of can take part in several reactions that create and destroy ozone. One set of reactions involving atomic and molecular oxygen is known as the Chapman reactions. The reactions are named after Sydney Chapman (1888-1970) who first proposed them in 1930. In one reaction, an oxygen atom combines with O to form ozone. Alternately, it can recombine with another oxygen atom to produce an oxygen molecule or react with ozone to produce two oxygen molecules. These reactions are summarized as... 

The actual destruction of ozone in the stratosphere actually involves hundreds of different reactions. Besides the Chapman reactions and destruction by CFCs, many other chemical species can destroy ozone. In 1970, Paul Crutzen (193 3-) showed that nitrogen oxides could destroy ozone. Nitric oxide can remove an oxygen atom from ozone and be regenerated according to the following reactions ... 

Chapman Reactions series of reactions responsible for the destruction of stratospheric ozone... 

Johnston, Crutzen, and others have also recognized that the natural ozone balance in the stratosphere cannot be explained on the basis of the Chapman mechanism and air motions. Johnston (542) has concluded that the calculated ozone destruction rate based on the Chapman reactions and air motions can explain only 20% of the natural destruction rate. About 80% of ozone produced by sunlight must be destroyed by a mechanism other than (VIII-43) and (VII1-44). 

The main set of reactions that describe the production and loss of ozone in the stratosphere are the Chapman reactions ... 

There can be no doubt that the inclusion of loss reactions other than the Chapman reaction has greatly improved the ozone balance in the stratosphere, but the consistency of the data in Table 3-4 should not be taken to... 

Table 3-4. Globally Integrated Stratospheric Loss Rates Due to the Chapman Reaction and Catalytic Destruction Cycles Involving CIO, NOx, and HOxa...

Chapman reactions and the various catalytic cycles varies with altitude and with the concentration of NOx, HOx, and halogen oxide gases. 

Ozone is produced by the photolysis of oxygen (by k < 242 nm UV radiation) and is readily reconverted to oxygen by the Chapman reaction of ozone with atomic oxygen. A simplified scheme of the photochemical equilibrium process for ozone formation is as follows. The concentration of ozone in the stratosphere is determined by the rates of chemical reactions that produce and destroy ozone. 

Until the early 1960s it appeared that these reactions could explain the main features of the steady-state distribution of ozone in the stratosphere. However, subsequent and more refined measurements of the rate coefficients for Reactions (7.24) to (7.27) showed that the Chapman reactions generate ozone five times faster than they destroy it. This is due primarily to the low value of in Reaction (7.27). Since the concentration of ozone in the stratosphere is not increasing at a rapid rate, there must be a much faster route for destroying ozone than indicated by the Chapman reactions. The search for this fast route, and the discovery of the sensitivity of stratospheric ozone concentrations to the presence of quite small amounts of certain trace... 

Fig. 1.1 Ozone Production and destruction rates, including absolute and relative contributions by the Chapman reaction R4 (Do), NO catalysis Rll + R12 (Dn), HO catalysis R5 + R6 (Dh) and ClOx catalysis R21 + R22 (DCl)x. The calculations neglect the heterogeneous halogen activation which become very important below 25 km under cold conditions...

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