Global Change: Ozone Depletion. Ozone or trioxygen ( O 3 ) is a triatomic molecule, consisting of three oxygen atoms. It is much less stable than the diatomic O 2 . Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals.
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Ozone or trioxygen (O3) is a triatomic molecule, consisting of three oxygen atoms. • It is much less stable than the diatomic O2. • Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals. • It is present in low concentrations throughout the Earth's atmosphere. • The ozone layer in the upper atmosphere filters potentially damaging ultraviolet light from reaching the Earth's surface.
“good” protective ozone “bad ozone”
Ozone depletion describes two distinct, but related observations: • a slow, steady decline of about 4 percent per decade in the total volume of ozone in Earth's stratosphere (ozone layer) since the late 1970s, and • a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. What’s the problem?
Since the ozone layer prevents most harmful UVB wavelengths (270–315 nm) of ultraviolet light (UV light) from passing through the Earth's atmosphere, observed and projected decreases in ozone have generated worldwide concern • It is suspected that a variety of biological consequences such as… • more melanoma and non-melanoma skin cancers • higher mutation rates • more eye cataracts • weakened immune systems • reduced plant yields • damage to ocean eco-ecosystems (kills plankton) • damage to plastics What are the ramifications of ozone depletion?
Destruction of ozone caused by atomic chlorine and bromine. • The main source of these atoms in the stratosphere is photodissociation of chlorofluorocarbon (CFC) compounds, commonly called freons, and of bromofluorocarbon compounds known as halons. • Used as flame retardants, fire extinguishants, refrigerants, propellants and solvents What are the Causes of Ozone Depletion?
These images from the Total Ozone Mapping Spectrometer (TOMS) show the progressive depletion of ozone over Antarctica from 1979 to 1999. This "ozone hole" has extended to cover an area as large as 10.5 million square miles in September 1998. The previous record of 10.0 million square miles was set in 1996. The Antarctic ozone hole develops each year between late August and early October. Regions with higher levels of ozone are shown in red
Ozone Depletion Potential (ODP): a number that refers to the amount of ozone depletion caused by a substance The ODP is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11. Ozone Depletion Potential
Chlorofluorocarbons (CFC’s) • contains: Cl, F, C • long-lived, non-toxic, non-corrosive, and non-flammable • High ODP • in 1960’s used in refrigerators, air conditioners, spray cans, solvents, foams • phase out by 1996 in developed countries Ozone Depleting Substances
Hydrochlorofluorocarbons (HCFCs) • contains: H, Cl, F, C • first major replacement for CFC • ODP’s range from 0.01 - 0.1 • much less destructive but also ozone depleting • reduce HCFC’s by 35% by 2004 in developed countries • Hydrofluorocarbons (HFC) • contain: H, F, C • do not deplete O3
Halons • VERY high ODP • contain: Br, Cl (in some but not all), F, H (in some but not all), C • Br many times more effective in destroying O3 • used in fire extinguishers • phased out by 1994 • Methyl Bromide (CH3Br) • an effective pesticide, used to fumigate agricultural soil and products • ODP = 0.4 • production in US ended 12/31/2000
Observed and projected decreases in ozone have generated worldwide concern leading to adoption of the Montreal Protocol banning the production of CFCs and halons as well as related ozone depleting chemicals such as carbon tetrachloride and trichloroethane. • First adopted in 1989. Revised several times since. • It is believed that if the international agreement is adhered to, the ozone layer is expected to recover by 2050. Montreal Protocol
The Montreal Protocol is working. Global observations have shown that the combined abundance of anthropogenic chlorine-containing and bromine-containing ozone-depleting substances in the lower atmosphere peaked in 1994 and has now started to decline. • Source: http://www.al.noaa.gov/wwwhd/pubdocs/Assessment98/executive-summary.html#A Good stuff
US EPA • web site: http://www.epa.gov/ozone/ • NASA • web site: http://www.nas.nasa.gov/Services/Education/Resources/TeacherWork/Ozone/Ozone.homepage.html • Wikipedia • http://en.wikipedia.org/wiki/Ozone • http://en.wikipedia.org/wiki/Ozone_depletion • http://en.wikipedia.org/wiki/Montreal_Protocol Additional Resources