CHAPTER 2: PROTECTING THE OZONE LAYER

CHAPTER 2: PROTECTING THE OZONE LAYER

Emphasizing Essentials

1. a. Yes, this is over the detection minimum of 10 ppb. 0.118 parts O 118 parts O 3 = 3 or 118 ppb 1,000,000parts air 1,000,000,000 parts air b. Yes, this is well over the detection minimum of 10 ppb. 25 parts O 25000 parts O 3 = 3 or 25000 ppb 1,000,000 parts air 1,000,000,000 parts air

2. a. A unit expressing the concentration of ozone in Earth's atmosphere over a specified area. It’s symbol is DU. It is named for G. M. B. Dobson (1889 – 1976). One Dobson Unit is equivalent to about 2.69 × 1016 ozone molecules in a column with a cross section of 1 square centimeter. If 100 DU of ozone were brought to the Earth's surface, it would form a layer 1 millimeter thick. b. 320 DU indicates more total ozone overhead than 275 DU.

3. Ozone is O3 and oxygen gas is O2. Oxygen gas is very stable, has no odor; ozone has a very strong odor and is relatively unstable or reactive. Oxygen gas condenses and changes from a colorless gas to a light blue liquid at 183 °C and a pressure of 1 atmosphere (atm). Ozone liquefies at a higher temperature than does diatomic oxygen, changing its physical state from a gas to a dark blue liquid at 112 °C.

4. a. Yes, diamond and graphite are allotropes. They are two distinct forms of the same element, carbon. b. No, water and hydrogen peroxide cannot be allotropes because they are compounds, not elements. c. Yes, white phosphorus and red phosphorus are allotropes because they are two distinct forms of the same

element. Red phosphorus forms when several P4 molecules combine into a chain structure.

5. The “ozone layer” is found in the stratosphere at altitudes of 15 to 35 km.

6. a. The cubic meter with CO in it contains more molecules. b. 20:1

7. a. O; 8 p, 8 e b. N; 7 p, 7 e c. Mg; 12 p, 12 e d. S: 16 p, 16 e

8. a. Group 2A b. beryllium, Be; magnesium, Mg; calcium, Ca; strontium, Sr; barium, Ba; radium, Ra c. Be has 4 e; Mg has 12 e; Ca has 20 e; Sr has 38 e; Ba has 56 e; Ra has 88 e d. Each element in this group has 2 outer electrons.

9. a. helium, He b. potassium, K c. copper, Cu

10. a. 8 protons, 10 neutrons, 8 electrons d. 35 protons, 47 neutrons, 35 electrons b. 16 protons, 19 neutrons, 16 electrons e. 10 protons, 9 neutrons, 10 electrons c. 92 protons, 146 neutrons, 92 electrons f. 88 protons, 138 neutrons, 88 electrons

19 11. a. 9 F 56 b. 26 Fe 222 c. 86 Rn

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12. a. Ca b. N

c. Cl d. He

Cl Cl 13. a. 4 + 4(7) = 32 outer electrons Cl C Cl and Cl C Cl Cl Cl

b. 2(1) + 2(6) = 14 outer electrons H O O H and H O O H

c. 2(1) + 6 = 8 outer electrons H S H and H S H

d. 2(5) = 10 outer electrons N N and N N

e. 1 + 4 + 5 = 10 outer electrons H C N and H C N

f. 2(5) + 6 = 16 outer electrons N N O and N N O

g. 4 + 2(6) = 16 outer electrons S C S and S C S

14. O O O O O H O O

The oxygen atom has two unpaired electrons and the hydroxyl radical has one. Ozone has no unpaired electrons, and depending on the method of representation, oxygen gas may have two unpaired electrons or none, although experimental evidence shows O2 to have unpaired electrons. A resonance structure for ozone may be drawn, and this is not true for the other structures. The representations of the oxygen atom and the hydroxyl radical show that the octet rule is not satisfied, which explains the very reactive nature of these species.

15. a. Wave 1 has a longer wavelength than wave 2. b. Wave 1 has a lower frequency than wave 2. c. Wave 1 and wave 2 travel forward at the same speed.

1m 16. a. 2.0cm = 210 –2 m This wavelength is in the microwave region of the spectrum. 102 cm 1m b. 400 nm ! = 4 ! 10–7 m This wavelength is in the range of violet light in the visible region. 10 9 nm 1 m c. 50 µm ! = 5!10 –5 m This wavelength is in the infrared region of the spectrum. 106 µm 1m d. 150 mm = 1.5 10 –1 m This wavelength is in the UHF/microwave region of the spectrum. 103 mm

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c 17. c = v !" and v = ; c = 3.0 × 108 m.s–1 !

3.0!108 m "s –1 a. # = = 1.5!1010 s –1 2!10 –2 m

3.0 "10 8 m# s–1 b. ! = = 8" 1014 s –1 4 "10 –7 m

3.0!108 m "s –1 c. # = = 6!1012 s –1 5!10 –5 m

3.0!108 m "s –1 d. # = = 2.0!109 s –1 1.5!10 –1 m

18. E = h.v and h = 6.63! 10–34 J"s a. E = (6.63x10-34 J.s)(1.5x1010 s-1) = 1.0x10-24 J b. E = (6.63x10-34 J.s)(8x1014 s-1) = 5x10-19 J c. E = (6.63x10-34 J.s)(6x1012 s-1) = 4x10-21 J d. E = (6.63x10-34 J.s)(2.0x109 s-1) = 1.3x10-24 J The most energetic photon corresponds to the shortest wavelength, 400 nm.

19. This is the order of increasing energy per photon. radiowaves < infrared radiation < visible light < gamma rays

c 20. c = v !" and ! = ; c = 3.0 × 108 m/s v 3.0 "108 m/s ! = = 1.2 "10#1 m 2.45 "109 /s

21. a. UV-C < UV-B < UV-A b. UV-A < UV-B < UV-C c. UV-A < UV-B < UV-C

UV-C photon 22. Chapman Cycle Step 1. +

collisions, fast + Chapman Cycle Step 2. UV-B photons

collisions, slow Chapman Cycle Step 3. + +

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23. a. Cl, 7 outer electrons, Cl ; NO2 , 17 outer electrons, N O

ClO, 13 outer electrons, Cl O ; HO, 7 outer electrons, H O b. Each of these species has less than a full octet of outer electrons on one atom. Their reactivity’s are based on their inclination to attain a full octet of outer electrons for each atom capable of holding an octet.

24. NO in the stratosphere can act as a catalyst for the destruction of ozone. Although most of the NO in the stratosphere comes from natural origins, additional NO could be contributed directly to the stratosphere by supersonic transport (SST) planes. Before their grounding, the Anglo-French Concorde was the only commercial plane flying at such high altitudes.

25. a. The original measurements were obtained during flights of NASA’s ER-2 research airplanes carrying measuring instruments over the Antarctic region. b. Today these measurements are usually gathered from satellites.

26. The first graph is a more realistic representation of the relationship between the percent reduction in the concentration of ozone and the percent increase in UV-B radiation. As the ozone layer is depleted, the concentration of UV-B that can penetrate into the atmosphere rises. The second graph shows a type of inverse relationship, which is not substantiated by experimental facts.

H

27. a. Methane, CH4, has 4 + 4(1) = 8 outer electrons. H C H H H H

Ethane, C2H6, has 2(4) + 6(1) = 14 outer electrons. H C C H H H b. Fourteen different CFCs that can be formed from methane.

c. The most successful examples have been CFCl3 and CF2Cl2. These Freon® compounds were widely used in the U.S. as refrigerants, propellants, and blowing agents to produce foams. d. Although many compounds are synthesized and tested for appropriate properties, only a few have the right combination of low reactivity, heat of vaporization, and lack of flammability to find broad applications.

Concentrating on Concepts 28. Oxygen and ozone have slightly different boiling points and colors in the liquid phase. Ozone is more easily liquefied. Ozone is chemically more reactive than oxygen. Oxygen is necessary for life, but ozone in the troposphere is considered an air pollutant. However, ozone in the stratosphere helps to protect us from harmful ultraviolet rays of the sun. Oxygen also absorbs ultraviolet light, particularly highly energetic UV-C radiation, preventing it from reaching the earth’s surface.

29. Energy from lightning or from an electrical arc associated with a transformer can cause this chemical

change. Energy + 3 O2 → 2 O3

30. Ozone in the stratosphere is necessary for absorbing harmful UV radiation, but down in the troposphere it is harmful to living beings.

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31. Allotropes of oxygen have different molecular forms, O2 vs. O3 for example. Isotopes of oxygen differ in 18 the number of neutrons in the nucleus. For example, 8 O has 8 protons, 10 neutrons, and 8 electrons if 16 electrically neutral. 8 O has 8 protons, 8 neutrons, and 8 electrons when electrically neutral.

32. With respect to electron distribution, the Lewis structures of SO2 and ozone are identical. This should not be surprising as sulfur is in the same chemical family as oxygen, so it has the same number of outer

electrons. The difference is that the outer electrons in the sulfur atom in SO2 are further from the S atom nucleus than is the case for the outer electrons in the oxygen atoms in O3. This difference does not show in the Lewis structures. Here are the resonance structures. O O O O O O O S O O S O and

33. There are 3(6) = 18 electrons in each Lewis structure, so each does satisfy the octet rule. Resonance forms represent hypothetical extremes of electron arrangements, but there is experimental evidence that this molecule is bent. The first two resonance structures are consistent with these experimental results, but the equilateral triangle structure does not conform to experimental measurements made on this molecule.

34. The oxygen-to-oxygen bond lengths in ozone are expected to be intermediate between the single and double bond lengths. They will all be the same, for resonance structures represent the extremes of structure and the real molecule is a hybrid of the two.

35. Energy is directly related to the frequency of electromagnetic radiation and inversely related to the wavelength of electromagnetic radiation. Further, wavelength and frequency are inversely related.

36. Of these choices, radio waves have the lowest energy and therefore the least potential for damage to biological systems.

37. The energy of a photon of a radio wave is only about one ten-millionth of the energy of a photon of UV radiation. While UV radiation has sufficient energy to interact with melanin in skin pigments, radio waves do not.

38. The UV Index gives the maximum number of minutes that the average person should be outside without UV protection. This is considered a “moderate” value on the usual reporting scale for the UV index and is in the “orange” region in the newspaper report. Individuals have very different sensitivity to the suns rays, so you may well make a decision to limit your exposure or to increase protection by putting on sunscreen.

39. UV-C radiation is extremely dangerous, but this radiation is almost completely absorbed by stratospheric

oxygen, O2, as well as by ozone, O3, before it can reach the surface of the earth.

40. There is a steady-state process in which a dynamic equilibrium is established between the formation and the breakdown of ozone in the stratosphere. Unless there are disturbances to this system, the dynamic system remains in balance and there is no net change in the concentration of the major species involved.

41. Over time, winds drive CFCs to the stratosphere.

42. Step 1: photon (λ ≤ 242 nm) + O2 → 2 O Neither forms nor destroys

Step 2: O + O2 → O3 Forms ozone

Step 3: photon (λ ≤ 320 nm) + O3 → O2 + O Destroys ozone

Step 4: photon O3 + O → 2 O2 Destroys ozone

. 43. ClO takes part in a catalytic cycle so a few ClO species can destroy many O3 molecules.

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44. There are wide seasonal fluctuations in the temperatures and wind patterns in Antarctica. Development of polar stratospheric clouds of ice crystals during the long, dark, and still winter months provides reaction sites for the conversion of non-ozone depleting particles to reactive species. When the sun finally comes out in Antarctica in late September and early October, the UV radiation releases Cl. free radicals, initiating the destruction of ozone. The images of the “Purple Octobers” in 2.25 Consider This reflect those changes. The general extent of the depletion in the Northern Hemisphere is not as severe as in the Southern Hemisphere. Even the observed downward trend observed through 1994–1995 has reversed in more recent years. Scientists have not classified the ozone depletion over the North Pole as a “hole,” but are carefully monitoring the location and intensity of UV-B radiation being received. We have already observed that the main reason for the observed difference between the total ozone changes in the two hemispheres is that the atmosphere above the North Pole usually is not as cold as that over its Southern Hemisphere counterpart. Although polar stratospheric clouds have been observed in the Arctic (Figure 2.22), the air trapped over the Arctic generally begins to diffuse out of the region before the Sun gets bright enough to trigger as much ozone destruction as has been observed in Antarctica.

45. HFC-134a: F H

F C C F

F H F F C O 46. a. There are 4 + 3(7) + 6 = 31 outer electrons available. F

b. This free radical is quite reactive in the troposphere, so it does not last long enough to reach the stratosphere.

. . 47. BrO + ClO BrCl + O2 BrCl + E Br. + Cl. . . Br + O3 BrO + O2 . . Cl + O3 ClO + O2

Net reaction: 2O3 3O2

48. a. According to the original protocol and the 1990 amendment, we would never return to the 1980 effective chlorine concentration. According to the Copenhagen and Bejing amendments, our the effective chlorine concentration in our atmosphere would return to the 1980 levels around 2020.

b. The second graph shows the predicted increases of skin cancer cases according to the different amendments.

c. If the Copenhagen amendment brings us to zero emissions, there would be no need for future amendments.

49. a. The concentration of ozone drops in the first 10 km of the troposphere. Then, there is a region of increasing ozone concentration until about 20 km, followed by dropping concentrations to about 30 km. The maximum concentration of ozone between about 10 km and 30 km; this is what is meant by the “ozone layer.” At even higher altitudes, the concentration of ozone begins to fall sharply.

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b. There is no reason to start the x-axis at zero. The concentrations of interest are those in the troposphere and stratosphere. Those range from about 1016 to 1019 molecules per cubic meter. Zero concentration is not relevant, and would extend the x-axis, and therefore compress the area of interest.

50. a. Photographs are analog (a hardcopy recording and reproduction process) products and images are sensor captured digital products. As you know photographic film is exposed to light at certain camera settings (aperture & time) and the scene is recorded onto the hard copy film. Today, satellite images use an electronic sensor that is capable of capturing specific ranges of the electromagnetic radiation field (e.g. true color, false color, and thermal infrared as well as other specific portions of the electromagnetic radiation field as desired) and is recorded in a digital format. So in the short, we can say a photograph is an analog product and the satellite image is a digital product. There are of course many additional differences; however, one would need a specific book to list them all. b. The chapter opening images are digital images taken from a satellite.

Exploring Extensions 51. a. The number of electrons for each element in each group can still be predicted from the atomic number of each element. b. The predicted number of outer electrons for each element of each group can still be predicted from the group number, 1 in both cases. c. The predicted formula when each element joins with chlorine is more reliable for the elements in group 1A than for those in group 1B. In group 1A, each formula will be XCl; NaCl for example. In group 1B,

there is some variability. Copper can join with chlorine in one of two ways; CuCl or CuCl2. Silver usually joins chlorine to form AgCl. Gold joins chlorine to form either AuCl or AuCl3. This uncertainty in predicting the joining ability of the B group elements is at the heart of the complication alluded to in the text.

52. 5 + 3(6) + 1 = 24 electrons – – – O N O O N O O N O O O O

53. O2 , O3 and N2 all have even numbers of electrons in their Lewis structures. N3 would have an odd number of electrons, 15. Molecules with odd numbers of electrons are generally more reactive than those in which all electrons are present in pairs.

54. The term “ozone layer,” while in widespread use, brings an incorrect image of a physically thick blanket-like layer to mind. In fact, even in the stratospheric region of highest concentration, ozone’s concentration is typically less than 1 ppm and is not even the most abundant species in that region. The ozone does not completely block all UV radiation, such as a blanket might block all visible light. The ozone that is present, however, serves the essential function of helping to screen out UV-B and UV-C radiation, reducing these components of sunlight before they reach the earth, making the screen analogy more nearly useful.

55. a. Ozone is also an effective disinfectant. It has the ability to oxidize proteins and enzymes, thereby being effective against microbes, viruses, odors and some micro-pollutants. A special apparatus (an ozonizer) is used to generate the ozone. Because ozone production decreases as the gas temperature increases, a cooling system is also usually provided to ensure a low temperature. The ozone that is generated is bubbled through water to be treated. Air purification units create ozone by taking in air and passing an electrical charge across it, and O2 is converted to O3 which reacts with airborne pollutants.

b. From the Web site, http://shop.solardirect.com/product_info.php?cPath=27&products_id=64, we find:

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AirPure Ozone System Indoor Air Sanitizer Purifier

Ozone (O3) is nature's strongest sanitizer and air purifier. Employing efficient corona discharge technology, the Superior Aqua Ozone Air system eliminates by oxidation the source of air contaminants commonly found in today's home and office. The National Council on Clean Air has identified indoor air pollution as one of the top ten killers in the U.S. today. Ozone is nature's cleanser for air and water. It is an unstable three-part molecule of oxygen. When an ozone molecule attaches itself to a contaminant, its oxidation process totally destroys it. Residual ozone reverts back to pure oxygen making it environmentally friendly.

Ozone air treatment • Destroys odors; tobacco, smoke, pet, cooking, and chemical • Kills bacteria, airborne viruses • Removes allergy causing pollen and microbes • Prevents mold and mildew, the leading cause of Legionnaires • Disease • Eliminates toxic fumes from printing, plating processes, hair and • nail salons, septic tanks, etc.

c. From the Web site, http://www.lotusenergy.com/ozone.htm, we find:

The ozone water purifier is lightweight and easy to move. It is designed specifically to purify water in holding tanks and emergency storage water tanks. It can also be used to purify drinking water from well sources or city water supplies by removing undesirable tastes, odors, and colors.

Advantages of Ozone Water Treatment Systems

• Improved health standards and improve the taste and odor of potable water. • Very effective disinfectant and can kill or disable pathogens resistant to other treatment methods. • Simple to use and maintain and does not require high ongoing expenses or components such as filters or chemicals.

• Can be easily powered with any renewable energy system such as solar. • Is an advanced and mature technology and used to treat water for many years. • Can be used with water that is cloudy or discolored without pre-filtration. • Modular construction allows for easy swapping of any broken or malfunctioning parts.

56. a. One factor is the reactivity of the compound and another is the length of time it remains in the atmosphere. Even if a compound is comparatively nonreactive in the troposphere, if it remains in the atmosphere for a long time, it may circulate to the stratosphere where increased exposure to UV radiation can change its reactivity. b. Most HCFCs, developed as replacements for CFCs, would be expected to have ODP values lower than those of the CFCs. HCFCs tend to be somewhat more reactive in the troposphere and have less effect on the stratosphere. Their ODPs range from 0.01 to 0.11. c. HFCs were also developed as CFC substitutes. Without chlorine or bromine present, they generally do not have the potential to deplete stratospheric ozone. Their ODP values are 0.0.

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57. a. This is a possible Lewis structure. . b. If Cl2O2 is the actual molecule, then it will have to be broken down by UV photons to ClO free radicals before it can react with oxygen atoms as shown in equations 2.8 and 2.9. This would add one additional decomposition reaction in the catalytic destruction of ozone.

58. a. 90 + 12 = 102. The compound contains one carbon atom, no hydrogen atoms, and two fluorine atoms.

The chemical formula for CFC-12 is CF2Cl2.

b. CCl4 contains one carbon atom, no hydrogen atoms, and no fluorine atoms. Therefore, the code number for CCl4 is CFC-10. c. Yes the “90” method will work for HCFCs. 90 + 22 = 112, so HCFC-22 would be composed of one

carbon, one hydrogen, and two fluorine atoms and its chemical formula would be CHF2Cl. d. No this method will not work for halons as there is no guideline for handling bromine.

59. a. Halon-1211 (CF2BrCl, a liquid steaming agent) and Halon-1301 (CF3Br, a gaseous agent) have proven to be extremely effective fire suppressants, which leave no residue and are remarkably safe for human exposure. From protecting computer and communication rooms throughout the electronics industry, to numerous military applications on ships, aircraft and tanks, to ensuring safety on all commercial aircraft, Halon has been an integral part of the safety plans in many of today's manufacturing, electronic, and aviation companies.Halon 1211 and 1301 stop the spread of fire by chemically interrupting combustion. Halons are odorless, colorless, electrically nonconductive, leave no residue after use and are "people safe."

The Montreal Protocol (1987 and subsequent) and the Clean Air Act Amendments (1990) identify Halon-1211 as a Class I ODS and established a ban on its domestic production effective 31 Dec 1993. Even though the use of Halons have been banned, their relatively long life (50-70 years) is expressed on the graph as we see that atmospheric abundance of halon-1211 peaked around 2002, and the prediction for the peak abundance of halon-1301 will be around 2015. Owners and users of Halon-1301 with "Critical Uses" may be able to claim exemption from the ban if the application is within the aircraft industry, military/armed forces, petrochemical industry and some marine applications; basically use that can claim to be connected with national security. The very high cost of replacing many existing halon systems with substitutes, replacements or other alternative fire protection measures continues to be a major impediment to eliminating continued use of halons.

b. By international agreement, however, production of all types of Halons ceased in 1994, but reserve banks and recycled Halons may still be used (see part a).

c. The small decline in total global consumption of methyl bromide is attributed largely to reductions for soil fumigation. The reason we expect to continue to see high concentrations of atmospheric CH3Br is that no existing technical alternatives for about 3,200 metric tonnes of MB per annum used for agricultural purposes have been found yet.

60. a. Australia has the highest incidence of skin cancer in the world and, on a national scale; more melanomas are reported in Queensland than anywhere else. Such a high rate of skin cancer in Australia may be attributable to a number of things: attitude, geological circumstance and Australian's love of the outdoors. There is still evidence that many Australians don't use effective sun-blocking aids.

Those who work outdoors, such as laborers, are more likely to develop skin cancer, according to the Australian National Occupation Health and Safety Commission. Also, people with fair skin are at a much higher risk of developing a skin cancer as opposed to those with darker skin.

b. At the start of the Australian Cancer Council 2004 SunSmart season Professor David Hill, Director of the Cancer Council, released the latest skin cancer rates and warned of the human and economic costs to all

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Australians if skin cancer rates continue to increase. One of the most successful health campaigns in Australia’s history was launched in 1981, when a cheerful seagull in board shorts, t-shirt and hat tap-danced his way across TV screens singing a jingle:

Slip, Slop, Slap! It sounds like a breeze when you say it like that Slip, Slop, Slap! In the sun we always say "Slip Slop Slap!"

Slip, Slop, Slap! Slip on a shirt, slop on sunscreen and slap on a hat, Slip, Slop, Slap! You can stop skin cancer - say: "Slip, Slop, Slap!"

The Slip Slop Slap slogan has become institutionalized, as the core message of The Australian Cancer Council’s SunSmart program for schools and local communities.

c. Facts stressed: Australians have the highest rate of skin cancer in the world. Each year over 1300 Australians die from this almost totally preventable disease. Luckily, actions to reduce risk of developing skin cancer are simple and effective.

d. Australian migrants, although having a significantly lower risk of skin cancer than people born in Australia, can still develop the disease. British and European migrants have the highest risk, followed by Southern European and Middle Eastern migrants.

e. Australian Aborigines, who have the darkest skin of all people living in Australia, while rare, may develop skin cancer. The darker the skin, the lower the risk of developing skin cancer. Those with fair, sensitive skin who burn easily and rarely tan are at greatest risk.

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