BrOx cycle

Chlorine nitrate CIONO2 and bromine nitrate B1ONO2 are important reservoir molecules formed by the chain termination reactions, CIO + NO2 and BrO + NO2, in the CIO and BrOx cycles in the stratosphere, respectively. Iodine nitrate IONO2 plays a similar role in the in the iodine chemistry in the troposphere. 

Therefore, HBr cannot be an important reservoir, and the efficiency of reaction (8.93) for the chain termination of the BrOx cycle is not very high. 

Figure 8.6 compares the vertical profiles of the O3 desfruction rates by each of the Ox, HOx, NOx, ClOx and BrOx cycles, calculated by a model considering all the reactions mentioned in Sects. 8.1, 8.2 and in this section, with those values calculated based on the observed values of radicals by a balloon (Osterman et al. 1997). As shown in the figure, these gas phase chain cycles cause large O3 destruction above 30 km in the upper stratosphere, and in the middle and lower stratosphere below 30 km the dissipation rate is less than 2 x 10 molecules cm s . Figure 8.7 shows the relative contribution of each cycle to the O3 destruction (Osterman et al. 1997). As shown in Fig. 8.7, the contribution of HOx is the most important in the upper stratosphere above 40 km and also in the lower stratosphere... 

Because NO plays such a small role in the removal of 03 in the lower stratosphere, its effects in this region arise primarily because of its interactions with the halogen and HO,. cycles that do control 03 loss here. Thus NOz interferes with the CIO, and BrOx... 

The atmospheric chemistry of the organobromides is similar to that of the organochlo-rides degradation ultimately produces bromine atoms which may participate in catalytic destruction of ozone through a BrOx catalytic cycle (reactions 12 and 13). 

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