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AIR ENVIRONMENT
CHAPTER 20 Climate Change and Ozone
WHAT IS OZONE? Oxygen
At sea level, 21% of air is diatomic oxygen Two oxygen atoms bonded together = O2
Ozone Triatomic form of oxygen (O3) Three atoms of oxygen bonded together Reactive molecule that is a strong oxidant and reacts
with many materials in the atmosphere
WHAT IS OZONE? The Ozone Layer
About 90% of ozone in the atmosphere is found in the stratosphere
Absorbs most (about 99%)of the ultraviolet radiation heading towards Earth UV radiation comes in three forms UVC
Shortest wavelength Most energetic Absorbed strongly in
atmosphere Negligible UVC reaches surface of
Earth
WHAT IS OZONE? UVA
Longest wavelength Least energetic Can cause some
damage to living cells Not affected by ozone
and is transmitted to Earth
UVB Intermediate wavelength Fairly energetic Strongly absorbed by
ozone layer Damaging to living cells THIS IS THE OZONE
PROBLEM
THE PROBLEM British Antarctic Survey began measuring ozone in 1957
From 1957 to 1970 the ozone concentration was fairly stable In 1984, the concentration took a sharp decline Their research indicated that stratospheric ozone concentration
has been decreasing Additional studies confirmed their reports Since then, this decline has been named the “Ozone
Hole” Not actually a hole Relative depletion in the concentration of ozone that occurs
during the Antarctic spring
THE PROBLEM Antarctic Hole
Each spring, the ozone in the Antarctic atmosphere decreases Amount of depletion has varied from 15%
to 80% In general, the thickness of the ozone layer
above the Antarctic each spring has been declining
Geographic area covered by the ozone hole continues to increase Covered 1 million or so square kilometers
in 1970 Today it covers over 22 million square
kilometers Larger than the entire U.S. and Canada
combined In 2000, it covered over 28 million square
kilometers Arctic Hole
Ozone depletion occurs over North Pole as well
Troublesome because it tends to spread
CAUSES Hypothesis that ozone is being depleted by the
presence of CHLOROFLUOROCARBONS (CFCs) was first suggested in 1974 CFCs have a long residence time in the lower atmosphere CFCs eventually make their way
to the upper atmosphere Here, they are destroyed by
solar UV radiation This process produces
chlorine, a highly reactive atom
Chlorine destroys ozone
CAUSES CFCs come from a variety of sources
Aerosol propellants in spray cans Working gas in refrigeration and air-conditioning units Foam-blowing process for production of styrofoam Cleaning computer parts during manufacture
Even if all manufacture, use and emission of ozone depleting chemical occurred today, the problem would not be solved CFCs remain in atmosphere between 74 and 140 years About 35% of certain types of CFCs will still be in air until 2100 Another 15% will be around till 2200 Some CFCs have not been emitted yet
EFFECTS OF DECREASED OZONE Marine Ecosystems Phytoplankton form the foundation of aquatic food
webs Exposure to solar UVB radiation has been shown to
negatively affect phytoplankton One study has indicated a 6-12% reduction This results in reduction in the size of the population of
animals that eat these smaller creatures
EFFECTS OF DECREASED OZONE Plants Plant growth can be directly affected by UVB radiation May result in decreased production
EFFECTS OF DECREASED OZONE Biogeochemical Cycles Increases in solar UV radiation could affect terrestrial
and aquatic biogeochemical cycles May result in increased levels of carbon dioxide (CO2),
and carbon monoxide (CO) Could increase effects of global warming
EFFECTS OF DECREASED OZONE Materials Synthetic polymers, naturally occurring biopolymers,
as well as some other materials of commercial interest are adversely affected by solar UV radiation
Any increase in solar UVB levels will therefore accelerate their breakdown, limiting the length of time for which they are useful outdoors
EFFECTS OF DECREASED OZONE Human Health Increases in type of skin cancer
1% decrease in ozone = 1% - 2% increase of UVB This will result in about 2% increase of skin cancer
Increase in a variety of diseases Eye damage Damage or reduce efficiency of human immune
system
http://www.epa.gov/ozone/science/missoz/index.html On The Trail of the Missing Ozone……