Summary Of Stratospheric Ozone Depletion

Figure 5.28 shows the total ozone loss rate as a function of altitude. Chemical destruction of 03 in the lower stratosphere (< 25 km) is slow. In this region of the stratosphere, 03 has a lifetime of months. Rates exceeding 106 molecules cm-3 s_1 are achieved only >28 km. Figure 5.29 gives the fractional contributions of the O*, NO*, HO*, and halogen cycles to the total ozone loss rate. In many respects, Figures 5.28 and 5.29 represent the culmination of this chapter—the synthesis of how the various ozone depletion cycles interact at

Fraction

FIGURE 5.29 Vertical distribution of the relative contributions by different catalytic cycles to the 03 loss rate (WMO 1998). [After Osterman et al. (1997) updated to current kinetic parameters.]

Fraction

FIGURE 5.29 Vertical distribution of the relative contributions by different catalytic cycles to the 03 loss rate (WMO 1998). [After Osterman et al. (1997) updated to current kinetic parameters.]

1990

1995

2000

1980 1985

FIGURE 5.30 Change in 03 column relative to 1980 value for the atmosphere between 60° S and 60°N. Measurements based on a variety of satellite and ground-based instruments (WMO 2002).

1990

1995

2000

1980 1985

FIGURE 5.30 Change in 03 column relative to 1980 value for the atmosphere between 60° S and 60°N. Measurements based on a variety of satellite and ground-based instruments (WMO 2002).

different altitudes in the stratosphere. Figure 5.30 summarizes global total ozone change relative to the 1964-1980 average.

In order to explain the fractional contributions in Figure 5.29 we can consider both the rate coefficients of the key reactions (Figure 5.31) and the profiles of O, N02, H02, 03, BrO, and CIO (Figure 5.32). The rates of the rate-determining reactions in each of the catalytic cycles can then be estimated at different altitudes. For example, at 15 km (!T ~ 215 K), the rates of key reactions (molecules cm-3 s-1) can be estimated as follows:

^no2+o= Wo[N02][0]^(1 x 10-11) x (4x 108) x (1 x 103)^5.0 Rno2+o,=kno2+o,[H02][03] (1 x 10"15) x (2 x 106) x (5 x 1011) £ 1 x 103 flcio+Bro^B,ci= wbro^Brci[C10][Br0]^(2x 10~12) X (1 x 103) X (2x 106)^3 x 10"3 flci0+Br0^ci00 = WBro^cioo[dO][BrO]^(8x 10"12) x (1 x 103) x (2x 106)=2x 10~2 *Bro+Ho2 = Who,[BrO][H02] ^(4 x 10"11) x (2 x 106) x (2 x 106)^2x 102

10-12

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