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