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FIGURE 3.31 Some values of 7(N02) measured using different techniques as a function of solar zenith angle: (a O) Kraus and Hofzumahaus (1998); (x) Madronich et al. (1983); (□) Brauers and Hofzumahaus (1992); (a) Shetter et al. (1992); (■) Lantz et al.

(1996); short dashed line is from Parrish et al. (1983);---is from

Dickerson et al. (1982) and solid line is from Müller and Schurath (1986). (Adapted from Kraus and Hofzumahaus, 1998.)

intensity at 200 nm. As discussed in Chapter 12, this is why chlorofluorocarbons, which absorb light in the 200-nm region, do not photodissociate until they reach the mid to upper stratosphere.

Figure 3.32 shows some calculated actinic fluxes in the stratosphere at 20-, 30-, 40-, and 50-km altitude at a solar zenith angle of 30° (DeMore et al., 1997) as well as at ground level. The surface albedo was assumed to be 0.3 and the aerosol concentrations typical of "moderate volcanic conditions."

The "window" in the stratosphere around 200 nm (where CFCs absorb) between the 02 and 03 absorptions (Fig. 3.13) is clearly evident in the actinic fluxes shown in Fig. 3.32. Figure 3.32 also clearly illustrates the tropospheric actinic cutoff of approximately 290 nm.

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