Nitrogen dioxide reaction mechanisms rate constants

Thus the lifetime of a constituent with a first order removal process is equal to the inverse of the first order rate constant for its removal. Taking an example from atmospheric chemistry, the major removal mechanism for many trace gases is reaction with hydroxyl radical, OH. Considering two substances with very different rate constants for this reaction, methane and nitrogen dioxide... 

For the reaction between nitrogen dioxide and carbon monoxide, the mechanism is thought to involve the steps shown in Fig. 15.8, where k1 and k2 are the rate constants of the individual reactions. In this mechanism gaseous N03 is an intermediate, a species that is neither a reactant nor a product but that is formed and consumed during the reaction sequence (see Fig. 15.8). 

Figure 22 presents the change of over-all reaction rate with change in partial pressure of carbon dioxide in the main gas stream. Nitrogen was used as the diluent, and the total flow rate was maintained constant. The over-all order of reaction is found to be ca. 0.5 from 950 to 1200°. An overall order of reaction of ca. 0.5 close to the start of Zone II has been interpreted to mean a true reaction order of zero (70, 79). In this case, however, as has been shown in Fig. 19, the true order is not zero at 1200°. Therefore, the above reasoning is not valid. An over-all order of 0.5 would be expected (for reaction in Zone II) if the mechanism of the reaction is represented by... 

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