Srp

FIGURE 6.31 Measured peroxy radical concentrations ([H02 ] + [R02]) and ozone photolysis rate 7(0'D) (a) or {7(0'D))115 (b) in clean marine air at Cape Grim, Tasmania (adapted from Penkett et al., 1997).

FIGURE 6.31 Measured peroxy radical concentrations ([H02 ] + [R02]) and ozone photolysis rate 7(0'D) (a) or {7(0'D))115 (b) in clean marine air at Cape Grim, Tasmania (adapted from Penkett et al., 1997).

Figure 6.31 shows plots of measured peroxy radical concentrations for low-NOx conditions at Cape Grim, Tasmania (Penkett et al., 1997). Overlaid are plots of /(O'D) and {/(O'D)}05. The plot of {/(O'D)}05 provides a better match. The slower decay in the peroxy radical concentration at dusk is due to the slow decay due to self-reactions, with some contribution from the CH302 + 03 reaction (k ~ fx 10"17 cm3 molecule"1 s"1; Tyndall et al., 1998) and perhaps a small contribution from deposition (Monks et al., 1996).

The relationship between {/(O'D)}05 and {[HOz] + [R02]} is better illustrated in Fig. 6.32, which shows plots of both the square root and first power of /(O'D) against the measured peroxy radical concentrations; the square root plot is linear, while the first-order plot curves significantly.

This chemistry suggests that under low-NOx conditions, there should be net photochemical destruction of 03 accompanied by the formation of peroxides. That is,

4 6 8 10 12 H02 + R02 (pptv)
0 0

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