Transcript
OZONEMary Lam
Fall 2011
What is Ozone?
Molecule containing three oxygen atoms unstable with respect to O2
Blue in color and has a strong odor Very reactive gas, and even at low
concentrations it is irritating and toxic Very powerful oxidizing agent
Ozone
Occurs naturally in small amounts in upper atmosphere and in the air of the lower atmosphere after a lightning storm.
Oxidizes many organic compounds Powerful germicide, used to sterilize air
and drinking water
Formation of Ozone
Ozone can be formed when a mixture of O2 and NO2 is exposed to bright light.
Such mixtures occur in the polluted air of large cities.
Earth’s Atmosphere
Found in layers
- Troposphere: lowest region, extends from the Earth's surface up to about 10 kilometers (km) in altitude.
-The next layer, the stratosphere, continues from 10 km to about 50 km.
Environmental Issues Photochemical
“smog”/ pollution Health problems Greenhouse gas Loss of ozone
layer
Ground-Level Ozone
In the troposphere, ground-level or "bad" ozone is a pollutant that is a significant health risk
It damages crops, trees and other vegetation. It is a main ingredient of urban smog.
Ozone Pollution
A concern during the summer months because strong sunlight and hot weather result in harmful ozone concentrations
Ozone Alert The concentration of ozone in the air can reach
levels that are dangerous for plants and animals. The U.S. Environmental Protection Agency
characterizes ozone levels as "unhealthful" when they exceed the National Ambient Air Quality Standard of 125 parts per billion (ppb).
In addition to posing a threat to health, ozone in the air also damages polymeric materials such as rubber and plastics, causing them to deteriorate prematurely.
Stratosphere Most atmospheric ozone is concentrated
in a layer in the stratosphere
Stratospheric Ozone
The stratosphere, or "good" ozone layer protects life on Earth from the sun's harmful ultraviolet (UV) rays.
Was gradually depleted by man-made chemicals like chlorofluorocarbons (CFCs).
A depleted ozone shield allows more UV radiation to reach the ground.
Greenhouse Gas Ozone is also a greenhouse gas in the
upper atmosphere and, therefore, plays a role in Earth's climate.
The increases in primary greenhouse gases, such as carbon dioxide, may affect how the ozone layer recovers in coming years.
Ultraviolet Radiation Protection
Absorbs a portion of the radiation from the sun, preventing it from reaching the planet's surface
Most importantly, it absorbs the portion of ultraviolet light called UVB.
UVB has been linked to many harmful effects
Ozone-Depleting substances (ODS) Chlorofluorocarbons (CFCs) Other chlorine-containing compounds
include methyl chloroform, a solvent, and carbon tetrachloride, an industrial chemical.
Halons, extremely effective fire extinguishing agents, and methyl bromide, an effective produce and soil fumigant, contain bromine.
Chlorofluorocarbons
Stable, low in toxicity, and inexpensive to produce
Noncorrosive, nonflammable Used as refrigerants, solvents, foam
blowing agents, and in other smaller applications
Used in fire extinguishers, as propellants in aerosols, solvents in electronics manufacture, and as foaming agents in plastics.
Ozone Depletion
The CFCs are so stable that only exposure to strong UV radiation breaks them down.
When that happens, the CFC molecule releases atomic chlorine.
One chlorine atom can destroy over 100,000 ozone molecules. The net effect is to destroy ozone faster than it is naturally created.
Ozone Hole
An annual ozone “hole” has been documented over Antartica every spring since the early 1980s.
Ozone depletion is focused mainly over Antarctica, and to a lesser degree the North Pole.
Montreal Protocol
Discontinue the production of CFCs, halons, carbon tetrachloride, and methyl chloroform and industry has developed more "ozone-friendly" substitutes.
Montreal Protocol is widely considered to be the most successful of the global environmental treaties.
The ozone layer is expected to recover over the next 50 years or so.
If CFC’s Weren’t Regulated…
http://www.youtube.com/watch?v=P-VZ3q7tbag
Expected Learning Outcomes Discuss the differences between “good”
and “bad ozone” Discuss how ozone is produced by
human activity Discuss the Montreal Protocol
Bibliography
http://scifun.chem.wisc.edu/chemweek/ozone/ozone.html
http://www.ozonelayer.noaa.gov/science/basics.htm
http://www.epa.gov/oar/oaqps/gooduphigh/bad.html#6
http://www.oar.noaa.gov/climate/t_ozonelayer.html
http://www.eoearth.org/article/Montreal_Protocol_on_Substances_that_Deplete_the_Ozone_Layer
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