Stratosphere and Ozone

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Geraldine Norris
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1 Stratosphere and Ozone

2 Ozone (Greek, ozein, to smell) O 3

4 Chapman Mechanism O 2 + hv O + O O + O 3 2O 2 O 3 + hv O 2 + O O + O 2 + M O 3 + M third-body. anything

5 What units are used to report the amount of the ozone? Dobson: named for G.M.B. Dobson who investigated atmospheric ozone ~( )

6 Dobson: compress all the ozone in a column down to 0 o C and 1 atm and measure the thickness of the column. 0.01mm = 1 Dobson

7 Catalytic Ozone Depletion Cycles X + O 3 XO + O 2 XO + O X + O 2 Net: O + O 3 O 2 + O 2 X=H, OH, NO, Cl

8 Altitude / km 60 The Ozone Layer Ozone Mixing Ratio Log Ozone Number Density Ozone Mixing Ratio / ppm Log Ozone Number Density / cm -3

9 The Ozone Layer and UV Radiation

10 Solar Flux: 5800 K Object Actinic Flux [photons cm -2 s -1 nm -1 ] energy of a C-H bond energy of ON-O bond Wavelength (nm)

11 Beer s Law A c l : extinction coefficient c: concentration l: path length

12 Hartley Band Ozone Absorption Absorption Cross Section [cm 2 ] Huggins Band Chappius Bands Wavelength (nm)

13 Solar Flux: 5800 K Object Actinic Flux [photons cm -2 s -1 nm -1 ] km Wavelength (nm)

14 Solar Flux: As you Move to Ground Level Actinic Flux (photons s -1 cm -2 ) km 0 km

15 Solar Flux: 5800 K Object Actinic Flux [photons cm -2 s -1 nm -1 ] UVC UVA UVB are very strongly affected by ozone levels, so that the levels of UVC radiation reaching the earth's surface are relatively small. strongly affected by ozone levels. Decreases in stratospheric ozone mean that more UVB radiation can reach the earth's surface, causing sunburns, snow blindness, immune suppression, and a variety of skin problems including skin cancer and premature aging. only slightly affected by ozone levels. Most UVA radiation is able to reach the earth's surface and can contribute to tanning, skin aging, eye damage, and immune suppression Wavelength (nm)

16 Catalytic Ozone Depletion Cycles X + O 3 XO + O 2 XO + O X + O 2 Net: O + O 3 O 2 + O 2 X=H, OH, NO, Cl

17 HO x Cycle OH + O 3 HO 2 + O 2 HO 2 + O OH + O 2 Net: O + O 3 O 2 + O 2 O( 1 D) + H 2 O OH +OH H 2 O + hv OH + H

18 NO x Cycle NO+ O 3 NO 2 + O 2 NO 2 + O NO + O 2 Net: O + O 3 O 2 + O 2 O( 1 D) + N 2 O NO + NO N ( 4 S) + O 2 NO + O

19 Null Cycles NO + O 3 NO 2 + O 2 NO 2 + hv NO + O Net: O 3 + hv O 2 + O

20 Null Cycles NO 2 + O 3 NO 3 + O 2 NO 3 + hv NO 2 + O Net: O 3 + hv O 2 + O

21 Reservoirs ClO + NO 2 + M ClONO 2 + M Cl + CH 4 HCl + CH 3 NO 2 + NO 3 + M N 2 O 5 + M

22 Antarctic Ozone Hole

23 Correlation Between ClO and O3

25 Modeling the Antarctic 'ozone hole'

27 Nobel Prize in Chemistry

28 ClO x Cycles Cl + O 3 ClO + O 2 ClO + O Cl + O 2 Net: O + O 3 O 2 + O 2 CH 3 Cl + hv CH 3 + Cl CFCs + hv radical + Cl

29 Mixing Times and Transport Vertical Mixing within Troposphere: weeks Mixing within Hemispheres: months Mixing between Hemispheres: ~1 year Mixing between Stratosphere and Troposphere: years

30 Ozone Depletion by CFC's CFC-12 chlorofluorocarbons CF 2 Cl 2 + hv CF 2 Cl + Cl Cl + O 3 ClO + O 2 ClO + O Cl + O 2 Net: O + O 3 O 2 + O 2

31 Nomenclature for CFC's CFC-xyz x: number of carbon atoms - 1 y: number of hydrogen atoms + 1 z: number of F atoms CFC-12 CF 2 Cl 2 CFC-115 CF 2 ClCF 3 (C 2 F 5 Cl)

32 Lifetimes of CFC's in the Atmosphere Halocarbon Atmospheric Lifetime (yr) CFCl 3 60 CF 2 Cl CF 2 ClCFCl CF 2 ClCF 2 Cl 236 CF 2 ClCF 3 522

33 Reservoirs ClO + NO 2 + M ClONO 2 + M Cl + CH 4 HCl + CH 3 NO 2 + NO 3 + M N 2 O 5 + M

34 Polar Vortex < 193 K 30 km PSC Tropopause Antarctica

35 Role of PSCs HCl + ClONO 2 Cl 2 + HNO 3 H 2 O + ClONO 2 HOCl + HNO 3 Cl 2 + hv Cl + Cl HOCl + hv Cl + OH

36 Atmospheric Chlorine Cycles HCl (het.) Cl 2 hv HOCl hv O 3 HO 2 HO 2 CH 2 O CH 4 H 2 Cl OH NO,hv,O,ClO,BrO hv hv ClONO 2 ClO NO 2 HCl H 2 O (het.) HCl (het.)

37 Mixing Times and Transport Vertical Mixing within Troposphere: weeks Mixing within Hemispheres: months Mixing between Hemispheres: ~1 year Mixing between Stratosphere and Troposphere: years

38 Ozone Depletion by Methyl Bromide Pesticide, kilotons/yr due to agriculture CH 3 Br Br Br + O 3 BrO + O 2 BrO + O Br + O 2 Net: O + O 3 O 2 + O 2

39 Sources of Atmospheric Bromine CH 3 Br CBrF 3 CBrClF 2 C 2 Br 2 F 4 CH 2 BrCl CHBrCl 2 CHBr 2 Cl CHBr 3 CH 2 BrI CH 2 Br 2 halons, anthropogenic sources natural sources, phytoplankton and microalgae

40 Coupling of Br and Cl Cycles Br + O 3 BrO BrO + O Br + O 2 O + O 3 O 2 + O 2 BrO + ClO Br + Cl + O 2 Br + O 3 BrO + O 2 ClO + O 3 ClO + O 2 O 3 + O 3 O 2 + O 2 + O 2

41 The Montreal Protocol Perhaps the single most successful international agreement to date has been the Montreal Protocol. -Kofi Annan, Secretary General of the United Nations Ozone Depleting Substances Developed Countries Developing Countries Chlorofluorocarbons (CFCs) Phased out end of 1995 Total phase out by 2010 Halons Phased out end of 1993 Total phase out by 2010 Carbon tetrachloride Phased out end of 1995 Total phase out by 2010 Methyl chloroform Phased out end of 1995 Total phase out by 2015 Hydrochlorofluorocarbons (HCFCs) Freeze from 1996 Freeze in % reduction by % reduction by % reduction by 2015 Total phase out by 2020 Total phase out by 2040 Hydrobromofluorocarbons (HBFCs) Phased out end of 1995 Phased out end of 1995 Methyl bromide Freeze in 1995 at 1991 level Freeze in 2002

42 Atmospheric Chlorine Loading Atmospheric Chlorine Loading (ppbv) Montreal 1987 London 1989 Copenhagen Year Critical Cl level

43 Lifetimes of HCFC's in the Atmosphere HCFC Atmospheric ODP Lifetime (yr) HCFC HCFC HCFC-141b HCFC-142b HCFC-225ca ODP (Ozone Depletion Potential): Relative to CFC-11

44 Ozone Depletion is Good for You: The Montreal Protocol was adopted with no consideration whatsoever of the benefits of UV exposure. For most land vertebrates including man, the only source of vitamin D-required for the metabolism of calcium into bone-is derived from the action of UV on the oils in the skin, fur, or feathers. (Furred and feathered creatures get their vitamin D by self-grooming). A shortage of vitamin D during the period of formation of the skeleton leads to rickets in the young and to osteoporosis in the old. Among the estimated 25 million people in the U.S. suffering osteoporosis today, there are approximately twice as many bone fractures per year, typically of the femur, as there are new cases of skin cancer. Theoretically, increased UV flux, as from decreases in the thickness of the ozone layer, would alleviate this condition in future generations. Ellsaesser, Hugh W., "With Respect to the Ozone Hole-Gore is Part of the Problem" in John A Baden, editor, Environmental Gore: A Constructive Response to Earth in the Balance, Pacific Research Institute for Public Policy, 1994.

45 Do volcanoes, which release large quantities of HCl into the atmosphere, contribute more to stratospheric ozone depletion than anthropogenic sources?

46 Although volcanic eruptions release significant quantities of HCl, few are strong enough to reach the stratosphere. In addition, the amount of water released is 1,000 times greater and most HCl is rained out.

47 What effect does increased UV-B radiation have on amphibians? Could ozone depletion be responsible for the decline in the amphibian population?

48 UV-B radiation has been shown to affect the proportion of eggs which hatch in certain species. However, the amphibian decline is worldwide and areas of significant UV-B increase is restricted.

49 Is the increased UV- B radiation caused by ozone depletion blinding Sheep in Chile? "temporary cataracts" were reported to be affecting sheep grazing at high altitudes in the spring

50 Johns Hopkins researchers has discovered that the blindness was the result of 'pink-eye'

Measurements of Ozone. Why is Ozone Important?

Measurements of Ozone. Why is Ozone Important? Anthropogenic Climate Changes CO 2 CFC CH 4 Human production of freons (CFCs) Ozone Hole Depletion Human production of CO2 and CH4 Global Warming Human change of land use Deforestation (from Earth s Climate: