Ozone Depletion, 2006, The size of the ozone hole = 28 million square km

1. Ozone Depletion, 2006, The size of the ozone hole = 28 million square km Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

2. Antarctic Arctic Ozone loss Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

3. Ozone Layer: the Global Sunscreen • A band of the stratosphere (17-26 km) above the earth’s surface. • Formed from the interaction of of solar UV radiation with O2 gas: 3O2 + UV  2O3 • Blocks almost 99% of the harmful solar UV radiation => global sunscreen • In general, O3 concentrations are higher at the equator & diminish as latitude increases.

4. Ozone: the Global Sunscreen • Stratospheric ozone (beneficial O3): • O3 is described as the global sunscreen => • Allows life to exist on earth • Protect human from: sunburn, skin and eye cancer… • Prevent O2 in troposphere from being converted to photochemical “harmful” O3 • Tropospheric or photochemical ozone (harmful O3): • O3 is highly reactive => Damages the respiratory system, plants & material => pollutant • Human activities are • ↓ in the amount of ozone in the stratosphere especially above the poles  ozone depletion • ↑ the amount of ozone in the troposphere

5. What is the problem??? Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

6. Stratospheric Ozone Depletion • 1985: the British Antarctic Atmospheric Survey discovered that stratospheric ozone levels over the South Pole (Antarctica) were dropping rapidly during September & October every year when the sunlight returned after the cold winter (Antarctic spring) • This seasonal ozone thinning (depletion) has been occurring since at least 1976 mainly over the poles • 1988: A similar but less severe O3 loss was discovered over the Arctic (North Pole) during the Spring & early Summer. • So far, this seasonal O3 loss over the North Pole had been lower than that over the South Pole

7. Causes of Ozone Depletion • Chlorofluorocarbons (CFCs) are the major culprit; used as • Coolants in ACs & refrigerators (CFC-11 & CFC-12) • Solvents, spray propellants (aerosols), foam blowing agents, cleaners for electronic parts (computer chips), sterilants for hospital instruments • Characteristics: stable (noncreative), odorless, nonflammable, nontoxic, noncorrosive, & cheap • From dream chemicals, CFCs turned out to be powerful ozone depleters

8. Other ozone depleters • Carbon tetrachloride (toxic solvent): sterilants for hospital instruments • Methyl chloroform • Solvent in correction fluid; • Propellant in dry-cleaning sprays, adhesives sprays and other aerosols • Methyl bromide (fumigant used against weed & pest)

9. Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breaking off a chlorine atom and leaving CFCl2. Sun Cl Cl Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. C Cl F UV radiation Cl Cl O O The chlorine atom attacks an ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2). A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2. Cl Cl O O O O The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule(ClO). O Cl O O O Summary of Reactions CCl3F + UV Cl + CCl2F Cl + O3 ClO + O2 ClO + O Cl + O2 Repeated many times CFCs destroy ozone in a cyclic chain of chemical reactions & are extremely persistent (65-385 years in the stratosphere) During its journey in the stratosphere, each Chlorine atoms can destroy up (convert to O2) to 100,000 O3 molecules CCl3F + UV  Cl + CCl2F Cl + O3 ClO + O2 ClO + O  Cl + O2

10. Antarctic Arctic Seasonal Thinning of Ozone Over the Poles • During the long, dark winter months in the poles, the stratospheric air is isolated & very cold (-90oC) => formation of ice crystals at high altitudes that absorb & immobilize chlorine & ozone molecules • When sun returns in the spring chlorine is liberated=> an extensive ozone depletion process proceeds rapidly

11. Consequences of Ozone Depletion • Health problems: • Less stratospheric O3 => more UV light => more sunburns & eye & skin cancers, eye cataracts • More tropospheric O3 => eye & nose irritation, respiratory problem, reduced resistance to colds & pneumonia. • Economic & environmental problems • ↓ in crops yields • ↓ in forest & oceans (phytoplankton) productivity => • Disruption of food webs, ecosystems & seafood yields • ↓ in CO2 uptake => ↑ global warming => … • ↑ degradation of outdoor materials (paints, plastics…)

12. Structure of the human skin & effects of UV radiations

13. Skin cancer & eye cataract caused UV radiations Normal eye Eye cataract

14. Squamous cell Carcinoma • Arising from cells in upper Epidermis, • this cancer is caused by exposure to sunlight or tanning lamps. • Curable if treated early. • Grows faster than basal cell carcinoma & can metastasize. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

15. Basal cell Carcinoma • Most common skin malignancy • Caused by exposure to sunlight or tanning lamps. • Develops slowly. Rarely metastasizes • Is nearly 100% curable if diagnosed early & treated properly Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

16. Melanoma • Deadliest of skin cancers, • Involves melanocytes cells, which produce pigments. • It can develop from a mole or an unblemished skin, • grows quickly & can spread to other parts of the body (metastasize) Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

17. How Can we Protect the Ozone Layer Using substitutes to CFCs & other ozone depleters • Immediate actions have already been undertaken in 1989 (Helsinki)=> • CFCs have been replaced by HCFCs (hydrochlorofluorocarbons), which release much less chlorine per molecules (the search goes on…) • CFCs production fell by 93% between 1989 & 1999 • By 2050: the ozone will return to 1980 levels • By 2100: the ozone will return to pre-1950 levels • Copenhagen protocol in 1992: • Phasing out of key ozone-depleting chemicals (esp. CFCs) • Reimbursement of developing countries for the costs of complying with the international protocol • Historical precedent for global cooperation to avert potential global disaster

18. CFC Production