Terms in this set (19)
What is ozone? How is ozone related to molecular oxygen? How is ozone formed?
-Ozone or O3 is a triatomic form of oxygen where three atoms of oxygen are bonded
-It is a strong oxidant and chemically reacts with many materials in the atmosphere
What is the difference between tropospheric ozone and stratospheric ozone?
-Stratospheric ozone is the primary UV radiation screen that protects us
-Tropospheric ozone is a secondary pollutant contains smog ozone- toxic to humans, animals, and vegetation
How much of the ozone in the atmosphere is in the stratosphere?
How far above the Earth's surface is the "ozone shield?"
-The ozone shield is the layer in the stratosphere that absorbs most of the potentially hazardous UV radiation that enters Earth's atmosphere from the sun at about 10-50 km above the Earth's surface
What are the 3 forms of ultraviolet light reaching the atmosphere?
-UVC: shortest wavelength and most energy, can breakdown O2 (individual O may combine with O2), strongly absorbed in the stratosphere, and small amounts reach the surface of earth
wavelength: 0.2- 0.28 nanometers
-UVA: longest wavelength and least energy, can cause some damage to living cells, not affected by strat. ozone, and is transmitted to earth's surface
wavelength: 0.32- 0.4 nanometers
-UVB: energetic and strongly absorbed by strat. ozone, (less ozone= more UVB), most harmful form of UV radiation
wavelength: 0.28- 0.32 nanometers
Describe the processes that produce ozone in the stratosphere.
-Photo dissociation of the oxygen molecule O2 yields two atoms of oxygen. Each combines with a diatomic oxygen molecule to form ozone
What are the units for measuring stratospheric ozone?
-The Dobson Unit is commonly used to measure the concentration of ozone. 1 DU = 1 ppb O3
Explain why the "ozone hole" is not really a hole
-Satellite measurements of ozone prior to 1985 indicate a small reduction in ozone concentration, however the values were so low they were not believed. The depletion in ozone was dubbed the ozone hole. There is no actual hole in the ozone shield where all the ozone is depleted, rather the term describes the relative depletion in the concentration of ozone that occurs during the Antarctic spring.
What are the major features of the Molina and Rowland hypothesis on ozone depletion?
-ozone is being depleted by the presence of CFCs
-CFCs emitted in the lower atmosphere by human activity are very stable and unreactive (long ART)
-CFCs eventually wander upward and enter the stratosphere, where they may be destroyed by the high energy UV radiation to produce chlorine.
-The very active chlorine released may enter reactions that deplete ozone in the stratosphere.
-The result of the depletion of ozone is an increase in the amount of UVB radiation that reaches Earth's surface.
What are the major ozone depleting chemicals and how are/were they used?
-CFC-12: AC, refrigeration, aerosols
-CFC-11: foams, aerosols, refrigeration
How do CFC's reach the stratosphere?
-CFCs have a long residence time and are not very reactive in the lower atmosphere.
-They are eventually carried upward.
-What is the atmospheric residence time of CFCs? ~100 years
What are the reactions of the chemical cycle that can deplete ozone?
-Cl + O3 → ClO + O2
-ClO + O → Cl + O2
What is meant by a catalytic chain reaction?
-In the first reaction, chlorine combines with ozone to produce chlorine monoxide, which in the second reaction combines with monatomic oxygen to produce chlorine again. The chlorine can then enter another reaction with ozone and cause additional ozone depletion. This series of reactions is what is known as a catalytic chain reaction.
Where and why is ozone depletion the most severe?
-Spring season (October) of Antarctic, ozone is at its thinnest
Explain the role of the following in the formation of the Antarctic Ozone Hole:
-Polar vortex: during the polar winter, the Antarctic air mass is isolated from the rest of the atmosphere and circulates about the pole in what is known as the polar vortex. It rotates counterclockwise because of the rotation of earth in the southern hemisphere. The vortex forms as the isolated air mass cools, condenses, and descends.
-Polar Stratospheric Clouds: These have been observed for about 100 years at altitudes of about 20 km above the polar regions. The clouds are approximately 10-100 km thick and have an iridescent beauty.
How does the thinning of the ozone layer harm humans? How can humans protect themselves from UV exposure?
-Increased UVB exposure causes melanoma and other forms of skin cancer. People can shield themselves with zinc products (sunblock) and other forms of physically blocking rays, such as a hat.
What are the environmental effects of ozone depletion?
-Leads to a reduction in primary productivity in the Earth's oceans--loss of productivity of phytoplankton would have a negative effect on the entire marine food chain.
-Depletion of arctic ice
-Could potentially kill food crops such as wheat, rice and beans and cause a social disruption
What are some strategies being used to deal with stratospheric ozone depletion? What are the advantages and problems with the substitutes for CFCs?
-Substitutes for CFCS, Collection and Reuse of CFCs, Montreal Protocol
-HFCs and HCFCs can cause the same ozone depletions as well as other pollution problems
What is the Montreal Protocol?
-A 1987 treaty of 180 nations agreed to cut CFC production in half. Later, this called for a complete phase-out of CFC's by 2000. Certain developing countries refused to sign on such as India and China.