1. Ozone Chemistry and
Ozone Depletion

2. Aurora over Halley Bay Station, Antarctica, 75.6ºS 26.5ºE
Brunt Ice Shelf, Coats Land
105 days of continuous darkness
Population: 65 in summer, 15 in winter

3. The Four Principal Layers of the Atmosphere

5. UV rays
+
=
Molecular Oxygen Ozone
Oxygen Atoms Molecule
UV rays
+

6. UV rays
+
=
Molecular Oxygen Ozone
Oxygen Atoms Molecule
UV rays
+

8. Distribution of Ozone
100 60
Thermosphere
80 50
Altitude (miles)
Mesosphere 40
60
Altitude (km)
Ozone 30
Oxygen
40
20
90% of ozone is in the stratosphere
20
10
10% of ozone is in the troposphere Troposphere
0 0
0 2 4 6 8
Ozone (parts per million)

9. Ozone is the Earth’s natural sunscreen
100 60
Thermosphere
80 UVc - 100% Absorption 50
Mesosphere
UVb - 90% Absorption
Altitude (miles)
UVa - 50% Absorption & Scattering 40
60
30
40
20
20
10
Troposphere
0 0
0 2 4 6 8
Ozone (parts per million)

11. UV radiation
CCl3F(g) ---------> CCl2F(g) + Cl(g)
Cl(g) + O3(g) ----> ClO(g) + O2(g)
ClO(g) + O(g) ----> O2(g) + Cl(g)

12. Other gases
Methyl chloroform (CH3CCl3) Other halons
3400 1% HCFCs (e.g., HCFC-22 = CHClF2) 4%
20 Halon-1301 (CBrF 3)
4% CFC-113 (CCl2FCClF2)
5%
3000 7% Carbon tetrachloride 14%
(CCl4) Halon-1211 (CBrCIF 2)
12% 15
CFC-11 (CCl3F) 20%
2000 5-20%
23% 10 Methyl bromide (CH3Br)
CFC-12 (CCl2F2)
1000
5
32% 27-42% Very-short lived gases
Methyl chloride (CH3Cl)
Natural (e.g., bromoform = CHBr3)
sources 16% 15%
0 0

15. Ozone Hole as of September 2006