NATS 101 Ozone Depletion

1. NATS 101Ozone Depletion

2. Last air pollution topic we’ll cover is the ozone hole. Is stratospheric ozone good or bad? Why?

3. inversion isothermal 6.5oC/km Recall that the warming in the stratosphere occurs due to the photodissociation of O3 and O2. Photodissociation occurs because of absorption of the sun’s UV rays.

4. Ultraviolet (UV) Absorption UV Visible IR A reduction in O3 would increase the UV that penetrates to the surface Ahrens, p 36

5. Possible Harm from O3 Loss • UV damages DNA (genetic material) Damage to plants (including crops) Reduction in ocean phytoplankton-base of food chain and major sink of CO2 Human impacts include… Skin cancers Eye cataracts Immunity suppression

6. Disassociation of O2 absorbs UV < 0.2 m O2 + UV  O + O O3 forms when O2 and O molecules collide O2 + O  O3 Disassociation of O3 absorbs 0.2-0.3 m UV O3 + UV  O2 + O Balance exists between O3 creation-destruction CFC’s disrupts balance Natural Balance of Ozone Danielson et al, Fig 2.28

7. CFC’s make up many important products Refrigerants Insulation Materials Aerosol Propellants Cleaning Solvents Sources of Chlorofluorocarbons

8. Commonly Used CFC’s Name Formula Primary Use Residence Time (50% decrease) CFC-11 CCl3F Propellant ~55 years CFC-12 CCl2F2 Refrigerant ~100 years CFC-113 C2Cl3F3 Cleaning Solvent ~65 years It would take ~10 years for CFC levels to start falling if all production ceased today owing to leakage of CFC’s from old appliances, etc.

9. Chronology of Ozone Depletion 1881 Discovery of ozone layer in stratosphere 1928 Synthesis of CFC’s for use as a refrigerant 1950s Rapid increase in use of CFC’s 1974 Description of ozone loss chemical reactions 1979 Ban of CFC use in most aerosol cans in U.S. 1980s Growth of CFC use worldwide 1985 Discovery of Antarctic ozone hole 1987 Adoption of Montreal Protocol calling for a 50% reduction in use of CFC’s by 1998

10. Chronology of Ozone Depletion 1989 Confirmation of ozone declines in mid-latitudes of Northern Hemisphere and in the Arctic 1990 Montreal Protocol amended to require a complete phase out of all ozone depleting chemicals by 2000 1990 U.S. requirement for recycling of CFC’s 1992 Discovery of high levels of ClO over middle and high latitudes of Northern Hemisphere 1992 Further amendment of Montreal Protocol calling for an accelerated phase out by ozone depleting chemicals 2100 Time needed until ozone layer heals completely?

11. How O3 is Measured: Dobson Unit • Ozone can be measured by compressing all ozone in column to sea-level pressure. • One Dobson Unit (DU) corresponds to a 0.01 mm depth at sea-level temperature and pressure • The ozone layer is very thin in Dobson units. There are only a few millimeters (few hundred Dobsons) of total ozone in a column of air

12. Mean October Total Ozone Ozone < 220 DU Considered Hole O3 evolution over Antarctica during the period 1979-2008.

13. Conditions over Antarctica promote ozone loss. Circumpolar vortex keeps air over Antarctica from mixing with warmer air from middle latitudes. Temperatures drop to below -85oC in stratosphere. Chemical reactions unique to extreme cold occur in air isolated inside vortex. Ingredient #1 Polar Vortex Williams, The Weather Book

14. June: Winter begins Polar vortex strengthens and temperatures begin to fall. July-August: Temperatures fall to below -85oC Ice clouds form from water vapor and nitric acid. Chemical reactions that can occur on HNO3ice crystals, but not in air, free chlorine atoms from the CFC. Ingredient #2Polar-Stratospheric Clouds nacreous cloud

15. Chlorine atoms can be freed from CFC’s by UV reaction CCl3F + UV  CCl2F + Cl CCl2F2 + UV  CClF2 + Cl C2Cl3F3 + UV  C2Cl2F3 + Cl Once a chlorine atom is freed, it can destroy thousands of ozone molecules before its sequestering from the air Cl + O3 O2 + ClO ClO + O  O2 + Cl Chlorine acts as acatalyst Chemistry of the Ozone Hole CFC-11 Moran and Morgan, Fig 2.19

16. Annual Cycle of Ozone over SP Ozone time-height cross-section http://www.esrl.noaa.gov/gmd/dv/spo_oz/

17. Arctic O3 “Mini-Hole”? Trend of about 10% per decade?

18. Northern Hemisphere Ozone Loss Partial Skin Damage Risk About a 5% decrease in mid-latitudes Erythema: reddening of skin from ionizing radiation http://www.esrl.noaa.gov/gmd/about/ozone.html

19. Key Points: Ozone Hole • Chlorofluorocarbons (CFCs) disrupt the natural balance of O3 in S.H. stratosphere CFCs responsible for the ozone hole over SP! Responsible for lesser reductions worldwide. • Special conditions exist in stratosphere over Antarctica that promote ozone destruction: Air cools to -85oC inside circumpolar vortex Allows formation of HNO3 nacreous clouds

20. Key Points: Ozone Hole • CFCs stay in atmosphere for ~100 years One freed chlorine atom destroys thousands of O3 molecules before leaving stratosphere • Montreal Protocol mandated total phase out of ozone depleting substances by 2000. • Even with a complete phase out, O3 levels Would not decrease for another 10 years Would not completely recover for ~100 years

21. Anthropogenic Damage And a Greater World Promise • TheOzone Holeshowed unequivocally that humans and industrialization can damage the environment on a large scale. • TheMontreal Protocolshowed that the world community can come together to solve major global issues. A SUCCESS STORY

22. Montreal Protocol is A UNEQUIVOCAL SUCCESS STORY But… Corrective Measures Were Relatively Painless

23. Assignment for Next LectureClimate Variability, Climate Change • Reading -Ahrens 4th: 324-327, 373-399 5th: 334-337, 383-409 • Homework11 -D2L Due Friday May 7 4th-Pg. 399: 14.5, 6, 7, 10 5th-Pg. 412: 14.5, 6, 7, 10 Do Not Submit Homework on D2L