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……