Ozone Depletion

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What is ozone? How is ozone related to molecular oxygen? How is ozone formed?
Ozone is O3 instead of molecular oxygen, O2.
2NO + O2 -->2NO2
2NO2 --> NO + O
O + O2--> O3
Reacts with sunlight to break and re-create bonds continuously in the stratosphere.
What is the difference between tropospheric ozone and stratospheric ozone?
Tropospheric ozone is a pollutant (a secondary pollutant) that causes difficulty breathing and prolonged lung health issues, it disperses quickly and is not in nearly as high concentrations as
Strasopheric ozone, the "ozone shield" that protects life from harmful ultraviolet light. People want ozone to stay here.
How much of the ozone in the atmosphere is in the stratosphere?
90% of ozone found in the atmosphere is found in the stratosphere.
How far above the Earth's surface is the "ozone shield?"
About 10-20 km
What are the 3 forms of ultraviolet light reaching the atmosphere? What are their wavelengths and how is each form affected by stratospheric ozone?
UVC-has the shortest wavelength and is the most energetic type of ultraviolet radiation. Sufficient energy to break down diatomic oxygen in the stratosphere into two oxygen atoms. Each of these oxygen atoms combines with an O2 to create O3. Strongly and almost completely absorbed by the stratosphere
UVB-energetic and strongly absorbed by stratospheric ozone, ozone is the only kown gas that absorbs UVB, UVB is the hazard we discuss when we discuss the ozone hole.
UVA-has the longest wavelength and the least energy. Can cause some damage to living cells, is not affected by ozone layer, and is transmitted to the surface of the earth.
Describe the processes that produce ozone in the stratosphere.
UVC radiation hits an O2 molecule and breaks the bond between the two atoms. (the UVC ray is absorbed by the bond and does not make it to the earth's surface). The single O molecule is then free to bond with another O2 molecule to form O3. Thus, the creation and destruction of ozone in the stratosphere is a continuous process.
What are the units for measuring stratospheric ozone?
The Dobson Unit, or 1 ppb is the commonly used measurement of ozone concentrations.
Explain why the "ozone hole" is not really a hole.
There is no actually hole in the ozone layer; that is, a specific area that has no ozone in it. The "ozone hole" refers to the overal thinning of the earth's ozone layer during the Artic Spring.
What are the major features of the Molina and Roland hypothesis on ozone depletion?
-The CFCs emitted in the lower atmosphere by human activity are extremely stable. They are unreactive in the lower atmosphere and therefore have a very long residence time (about 100 years). There are no known signifigant tropospheric CFC sinks (except possibly the soil)
-CFCs eventually enter the stratosphere because of the fluidity of the atmosphere and their long average residence time. The sunlight they encounter here destroys CFC bonds and creates reactive chlorine.
-The reactive chlorine enters into reactions that deplete ozone in the stratosphere
-The result of the depletion of ozone is the amount of UVB raditation that reache's the Earth's surface. Cause of skin cancers and is harmful to the immune system.
What are the major ozone depleting chemicals and how are/were they used?
CFC-12---air conditioning, refridgeration, aerosols and foams
CFC-11---Foams, aeorsols, refridgeration
CFC-113/Carbon tetrachloride/Methyl chloroform---solvents
Halon 1301---Fire extinguishers
Halon 1211-Refridgeration, foams
HCFC-22/HCFC-123/HCFC-124---Substitute for CFC
How do CFC's reach the stratosphere?
CFCs have a very long average residence time of about 100 years. During this time in which they do not react, due to the fluidity of the earth's atmosphere, CFCs are eventually carried up to the stratosphere.
What is the atmospheric residence time of CFCs?
100 years or so.
What are the reactions of the chemical cycle that can deplete ozone?
Cl+O3-->ClO+O2 actual breaking down of ozone
ClO+O-->Cl+O2 preventing free O particles from binding with existing O2
What is meant by a catalytic chain reaction?
catalytic chain reaction--because the chlorine is not removed but reappears as a product of the second reaction, the process can repeat itself over and over again.
Where and why is ozone depletion the most severe? At what time of year is the ozone layer the thinnest and why?
Spring season (October) of Antartic, ozone is at its thinnest. Nitrogen oxides stirred up by polar vortex undergo the following reaction:
HCl+ClONO2-->Cl2+HNO3
NOx create the largest Chlorine sink by forming Chlorine nitrate and thereofore prevents the free Cl from destroying ozone. NOx are not present in the Artic vortex during the springtime (NOx precipitates out of the resulting heavy clouds). Also in the spring sunlight returns and breaks up the Chlorine again.
Polar vortex
arctic air masses that in the winter become isolated from the rest of the atmosphere and circulate about the pole; the vortex rotates counterclockwise because of the rotation of the Earth in the Southern Hemisphere. Cools, condenses, descends.
Polar Stratospheric Clouds
A cloud that forms at altitudes of about 21,000 m during the Artic and Antartic winter or early spring, when air temperature drop below -80*C
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 shield themselves with zinc products (sunblock) and other forms of physically blocking rays, such as a hat. Or they just don't go outside because they're too busy studying for their APES test anyway.
What are the environmental effects of ozone depletion?
-Leads to a reduction in primary productivity in the Earth's oceans--loss of poductivity of phytoplankton would have a neagtive effect on the entire marine food chain.
-Depletion of artic 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?
Susititues 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.
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