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Figure 4.16 shows a schematic of the interconversion pathways for the major members of NOv. NO, species interconvert rapidly compared to the time-scale with which NO,, is produced or destroyed, but slowly compared to the time-scale with which the members of NO, interconverts.

Formation of reservoirs from NOK NO, is converted to the various reservoir species primarily in three-body reactions. N ,Os is produced by the reaction

Because of the extremely low abundances of NO, during the day, this process is important only at night. This reaction consumes two NO, molecules for each N.O,, created. HNO, is produced from NO, by the reaction

ClONO, is formed from NO, in the reaction (4.10):

BrONO, is formed in an analogous reaction:

Formation of /VOx from reservoirs The destruction of these NOv reservoirs reforms NO, N,0, is destroyed by photolysis and thermal decomposition to reform NO,:

Thermal decomposition (reaction (4.45)) makes up ~\% of the loss of N,Os in the lower and mid-stratosphere, and as much as 10% in the upper stratosphere, owing to the warmer temperatures and lower pressure found there.

Figure 4.15 Fraction of NO, in the form of NO, NO,, and NO, derived from a model incorporating the J PI. 94 reaction set [91 J. Note that the NO, scale is on the right. "Upper stratosphere" is from the 3.16 hPa level of the model, "mid stratosphere" is 14.7 hPa, and "lower stratosphere" is 57.0 hPa. The model run is at 45°N on March 21, 1996 and using background aerosol abundances.

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