Ozone Chemistry and Ozone Depletion

Aurora over Halley Bay Station, Antarctica, 75.6ºS 26.5ºEBrunt Ice Shelf, Coats Land

105 days of continuous darknessPopulation: 65 in summer, 15 in winter

The Four Principal Layers of the Atmosphere

UV rays

Molecular Oxygen

Oxygen Atoms

+=

Ozone Molecule

UV rays

+

UV rays

Molecular Oxygen

Oxygen Atoms

+=

Ozone Molecule

UV rays

+

Ozone (parts per million)

0

20

40

60

80

100

Alt

itu

de

(km

)

Troposphere

Mesosphere

Thermosphere

Distribution of OzoneA

ltitud

e (miles)

10

0

20

30

40

50

60

90% of ozone is in the stratosphere

0 2 4 6 8

10% of ozone is in the troposphere

OxygenOzone

UVc - 100% AbsorptionUVb - 90% Absorption

UVa - 50% Absorption & Scattering

Ozone is the Earth’s natural sunscreen

Ozone (parts per million)

0

20

40

60

80

100

Troposphere

Mesosphere

Thermosphere

Altitu

de (m

iles)

10

0

20

30

40

50

60

0 2 4 6 8

CCl3F(g) ---------> CCl2F(g) + Cl(g)

UV radiation

Cl(g) + O3(g) ----> ClO(g) + O2(g)

ClO(g) + O(g) ----> O2(g) + Cl(g)

16%

32%

23%

12%

7%

5%

1%

4%

0

3400

3000

2000

1000

(CH3CCl3)

(e.g., HCFC-22 = CHClF2)

(CCl2FCClF2)

Naturalsources

Other gases

Methyl chloroform

HCFCs

CFC-113

Carbon tetrachloride

(CCl4)

CFC-11 (CCl3F)

CFC-12 (CCl2F2)

Methyl chloride (CH3Cl)

0

20

15

10

5

15%

27-42%

5-20%

20%

14%

4%

Methyl bromide (CH3Br)

Halon-1211 (CBrCIF2)

Halon-1301 (CBrF3)

Other halons

Very-short lived gases

(e.g., bromoform = CHBr3)

Ozone Hole as of September 2006