Atmosphere Composition of air Nitrogen (78%) Oxygen (21%) Water vapor (0.01-4%) Argon (< 1%) Carbon dioxide (0.037%)

Ozone Oxygen molecules interact with UV radiation from sun Keeps about 95% of the sun’s harmful UV radiation from reaching earth’s surface Stratospheric ozone is essential to life on earth Tropospheric ozone forms photochemical smog

UV and the Atmosphere

UV and Ozone Some UV radiation from the sun is absorbed by stratospheric ozone causing it to break apart. Under normal conditions the ozone molecule will reform This is a dynamic equilibrium

Ozone and Halogenated Organic Gases Halogens – Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At). Halogen atoms (such as chlorine) increase destruction of ozone in a repetitive cycle, allowing more UV radiation to reach the Earth

Ozone Depleting Substances CFCs (chlorofluorocarbons) Aerosols, gas-blown plastics, refrigerants Halons (fire extinguishers – release bromine atoms) Methyl Bromide (pesticide – releases bromine atoms)

CFCs Chlorofluorocarbons (CFCs)—stable, odorless, nonflammable, nontoxic, & noncorrosive chemicals Coolants in refrigerators & air conditioners (freon) Largest source - leaking car air conditioners Propellants in aerosol spray cans Cleaners for electronic parts such as computer chips

UV and Living Organisms The effects of UV on living tissues includes: Mutation during cell division Health effects (sunburn, skin cancer, eye cataracts, & damage to immune system) Damage to photosynthetic orgamisms (phytoplankton and their comsumers) Decreases productivity

Ozone Depletion CFC molecules break down under the influence of UV radiation releasing high energy chlorine atoms which speed up the breakdown of ozone into oxygen Causes ozone in various parts of the stratosphere to be destroyed faster than it is produced CFC molecules last on average 75-111 years Each chlorine molecule released can convert 100,000 molecules of ozone into oxygen video

Results of Ozone Depletion Increased UV radiation reaching earth’s surface Increase in acid deposition & photochemical smog Lower yields of key crops (corn, rice, cotton, soybeans, wheat) Decline in forest productivity (reducing CO2 uptake, enhancing global warming) Increased breakdown & degradation of paints, plastics, & outdoor materials Reduction in productivity of surface-dwelling phytoplankton in oceans

Solutions? Reduce manufacture and release of ozone-depleting substances Recycle refrigerants Alternatives to glass-blown plastics, halogenated pesticides, propellants and aerosols Develop non-propellant alternatives

Ozone Thinning 40-50% of ozone in upper stratosphere over Antarctica was destroyed after 1976 Takes 11-20 years for CFCs to reach the stratosphere Peak production of CFCs occurred in 1989 In 2000, ozone thinning above Antarctica covered an area 3x the size of the continental US

Montreal Protocol UNEP (United Nations Environment Programme) – provides information, forges international agreements, studies the effectiveness of these agreements, and the difficulties implementing and enforcing them Montreal Protocol on Substances that Deplete the Ozone Layer (1987) international agreement on reduction of use of ozone-depleting substances National governments complying with the agreement made national laws and regulations to decrease the consumption and production of halogenated organic gases (such as CFCs)

Montreal Protocol

Significance of Montreal Protocol The best example of international cooperation on an environmental issue An example of many experts in their different fields coming together to research the problem and find solutions The first to recognize that different countries could phase out ODCs at different times depending on their economic status The first with regulations that were carefully monitored

Unfortunately….. Though most countries followed the rules, China and India were still producing huge amounts of CFCs—their need for refrigerators and ACs is growing due to fast economic growth China has agreed to phase out ODC production 2 years ahead of schedule and India has as well Because CFS have a long life, chlorine did not reach its peak until 2005 It will take until 2050 to return to pre-ODC levels