Figure 3.5 Contours of annually averaged (a) O, production rate (in Kf molecules env * s"') and (b) O lifetime with respect to production ([O, [//*), in days. These calculations are from the Goddard two-dimensional climatological circulation model |73|.

30 km. Figures 3.5a and 3.6a show that the annually averaged production and loss rates are generally not equal. Production exceeds loss in the tropics, while loss exceeds production in the extratropics. Transport of O, from the tropics to higher latitudes closes the budget, and ensures that the annually averaged change of lower-stratospheric O, is close to zero. This will be discussed in detail in Chapter 5.

Above 30 km. the rates of production and loss are approximately equal. In this region, chemistry is much faster than transport of Oa, so we can assume that O, is in steady state. Between about I0 and 2 hPa, the lifetime of O, is greater than a day. so


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