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

Disruption of Biogeochemical Cycles Carbon cycle—addition of carbon dioxide to the troposphere mostly by burning fossil fuels Have potential to warm earth’s atmosphere Nitrogen cycle—release of nitrogen oxides & gaseous ammonia by burning fossil fuels and using nitrogen fertilizer Have the potential to lower pH of soils, streams, & lakes Sulfur cycle—release of sulfur dioxide from petroleum refining and burning of coal Forms sulfuric acid as a component of acid rain

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

UV and Ozone UV radiation is absorbed during the process of formation and destruction of ozone and oxygen O2 and O3 are continuously breaking down and reforming – dynamic equilibrium UV causes O2 to break down into monoatomic O Oxygen atoms are very reactive so they can combine with an oxygen molecule to form ozone (O3).

Ozone and Halogenated Organic Gases Halogens – Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At). Halogenated organic gases are stable unless exposed to UV – these released halogens react with monoatomic oxygen and slow ozone formation, disturbing the equilibrium

Sources CFCs (chlorofluorocarbons) HCFCs (hydrofluorocarbons) 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

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

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

Seasonal Ozone Thinning

Seasonal Ozone Thinning Steady winds create a circular pattern over the earth’s poles creating a polar vortex CFCs & ODCs cannot react with ozone in the dark, so they accumulate each winter Upon return of sunlight in spring, large numbers of chlorine atoms are released, destroying 40-50% of ozone above Antarctica When vortex breaks up, masses of ozone-depleted air move away from poles

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? Recycle refrigerants Alternatives to glass-blown plastics, alternative propellants (propane) Alternatives to methyl bromide Aerosol cans use liquified petroleum gas (LPG)

Montreal Protocol Montreal Protocol (1987) international agreement on reduction of emission of ozone-depleting substances (CFCs and later added halons) Most countries followed the rules but China and India continued to produce and use huge amounts of CFCs. But they have since both agreed to phase out the use of CFCs. unfortunately CFCs have a long lifespan and it has been estimated that the levels will not return to normal before 2050 London Agreement (1990) and Copenhagen Treaty (1992) offered more restrictions on CFC emissions video

Montreal Protocol