212
Chemical Oceanography, 4th Edition
Photodissociation or other free radical reactions can reverse these reactions:
OH· + HCl → H 2 O + Cl·
(5.38)
HNO 3 + hυ → OH· + NO 2
(5.39)
HO 2 + NO· → OH· + NO 2
(5.40)
OH· + CO → CO 2 + H·
(5.41)
With increasing CFC production (see Figure 5.33), one would expect that the formation of Cl by photodissociation would be more important in removing O 3 in future years.
Even though the aerosol usage of CFCs has decreased, nonaerosol usage has increased.
The increase of CFCs, methylchloroform, carbon tetrachloride, and nitrous oxides since
1978 has been documented by direct measurements (see Figure 5.34). The decrease in O 3
levels will increase the amount of UV radiation that reaches the earth. This is shown in
Figure 5.35. This plot includes all the wavelengths weighted according to how damaging
they are to biological systems (300 to 345 nm). A 100% decrease of O 3 will increase the
damaging UV flux by about 18%.
Recent attention to the destruction of O 3 has concentrated in the Antarctic region over the
years from 1960 to 1992 (see Figure 5.36) in the springtime. This has caused the so- called
ozone hole over the South Pole (Figure 5.37). This springtime loss of ozone extends well
north of Antarctica (see Figure 5.38). It should be pointed out that one Dobson unit equals
a concentration of O 3 of one molecule in every 10 9 total molecules. Work showed that the
size of the ozone hole increased considerably over the years 1980 to 2004 (see Figure 5.39).
Since the global concentrations of O 3 show large variations (see Figure 5.40), it is difficult
to distinguish trends over time.
Year
1960
1965
1970
1975
1980
1985
CFC Production (10
6
kg)
0
200
400
600
800
1000
Total
Nonaerosol
Aerosol
Figure 5.33
The production of chlorofluorocarbons (CFCs) from 1960 to 1985.
Chemical Oceanography, 4th Edition
Photodissociation or other free radical reactions can reverse these reactions:
OH· + HCl → H 2 O + Cl·
(5.38)
HNO 3 + hυ → OH· + NO 2
(5.39)
HO 2 + NO· → OH· + NO 2
(5.40)
OH· + CO → CO 2 + H·
(5.41)
With increasing CFC production (see Figure 5.33), one would expect that the formation of Cl by photodissociation would be more important in removing O 3 in future years.
Even though the aerosol usage of CFCs has decreased, nonaerosol usage has increased.
The increase of CFCs, methylchloroform, carbon tetrachloride, and nitrous oxides since
1978 has been documented by direct measurements (see Figure 5.34). The decrease in O 3
levels will increase the amount of UV radiation that reaches the earth. This is shown in
Figure 5.35. This plot includes all the wavelengths weighted according to how damaging
they are to biological systems (300 to 345 nm). A 100% decrease of O 3 will increase the
damaging UV flux by about 18%.
Recent attention to the destruction of O 3 has concentrated in the Antarctic region over the
years from 1960 to 1992 (see Figure 5.36) in the springtime. This has caused the so- called
ozone hole over the South Pole (Figure 5.37). This springtime loss of ozone extends well
north of Antarctica (see Figure 5.38). It should be pointed out that one Dobson unit equals
a concentration of O 3 of one molecule in every 10 9 total molecules. Work showed that the
size of the ozone hole increased considerably over the years 1980 to 2004 (see Figure 5.39).
Since the global concentrations of O 3 show large variations (see Figure 5.40), it is difficult
to distinguish trends over time.
Year
1960
1965
1970
1975
1980
1985
CFC Production (10
6
kg)
0
200
400
600
800
1000
Total
Nonaerosol
Aerosol
Figure 5.33
The production of chlorofluorocarbons (CFCs) from 1960 to 1985.