1. 1 Ozone Layer: Existence and Anthropogenic Depletion GLY 4241 - Lecture 7 Fall, 2016

2. 2 Atmospheric Layers

3. UV Wavelength Ranges UV-A 315-400 nm UV-B 280-315 nm UV-C 100-280 nm 3

4. Ultraviolet Radiation

5. Absorption of Solar Radiation 5

6. Effects of Increased UV Modify rate of photosynthesis  Marine phytoplankton  Terrestrial crop and plant damage Leads to increased CO 2 levels in the atmosphere Species specific effects – diatoms vs. phaeocystis 6

7. 7 Dimethylsulfide Causes that distinctive smell from boiled cabbage When this compound is present at low levels in wines, it contributes to an overall fruity odor Dimethyl sulfide given off by marine organisms is thought to be a source of cloud condensation nuclei, and this, in turn could affect the Earth's climate

8. 8 Foram

9. Coral Bleaching Since 1987, corals around the world have been ”bleaching.”  They suddenly lose their pigment The same phenomenon has been observed in forams, for the same reason The damage is due to increased UV levels, not higher water temperatures 9

10. UV-B Damage Increased levels of UV-B radiation has deleterious effects on living organisms, such as DNA damage When exposed to elevated ultraviolet-B radiation, plants display a wide variety of physiological and morphological responses characterized as acclimation and adaptation 10

11. 11 Morphological Differences Transgenic Arabidopsis thaliana plants (line A11) grown under different daily UV-B doses f-i, 23-day-old Arabidopsis, germinated and grown under 41 molm -2 d -1 photosynthetic active radiation with different daily UV-B doses. f, UV-B1 2.3 kJ/m 2 d g, UV-B2 6.6 kJ/m 2 d h, UV-B3 18.6 kJ/m 2 d i, UV-B4 27.1 kJ/m 2 d Scale is the same for f-i.

12. Concern About Ozone Loss Changes in the ozone layer became of concern in the 1970's Research on the ozone layer was spurred by perceived anthropogenic threats to the layer From 1977 to 1984 the ozone levels over Halley Bay, Antarctica decreased by 40% in the region from 12 to 24 kilometers The problem grew progressively worse into the early 1990's, and the area with the worst ozone depletion is in the Southern Hemisphere 12

13. 13 ER-2 Research This plane is similar to the U-2 spy plane, designed to fly in the stratosphere The air intake (the "football") is clearly visible as a shiny, oval, metallic sphere sticking out at the bottom, in front of the front wheel

14. UARS Upper Atmosphere Research Satellite Deployed by space shuttle Discovery om 9/15/91 UARS is perhaps best remembered for studies of the ozone layer and Antarctic ozone hole, particularly the role of chlorine, halocarbons, and nitrous oxides in ozone depletion The decommissioned satellite re-entered Earth's atmosphere on 24 September 2011 14

15. UARS Evidence In 1992, it was suggested that a hole does might develop over the Arctic, due to findings that suggested conditions favorable for substantial ozone reductions existed over northern Europe, roughly from London to Moscow (Kerr, 1992). At that time, it was suggested ozone losses might reach a depletion of 30-40%. Vogel (1993) stated that harmful ultraviolet striking the northern hemisphere rose 5% in the preceding decade 15

16. 16 Arctic Ozone Hole, 1999 The red color indicates high levels of ozone in Dobson units and blue, yellow, green are lower values In 1999, there was considerable ozone available in the Arctic

17. 17 Arctic Ozone Hole, 2000 In 2000, there is a large area of depletion (blue)

18. Arctic Conditions Changes during the winter months are large fractional increases in small values. Biologically, they may not be of great significance Increases during the spring and summer, although of smaller degree, may be more significant This increase is occurring when many species are reproducing and the biological effects may therefore be larger. 18

19. 19 Antarctic Ozone Hole Satellite maps of total ozone over Antarctica on September 24, when the ozone hole is near its annual peak

20. 2015 Ozone Hole 20 Latest current image 2016

21. A Threat That Did Not Happen Serious changes in the ozone levels in the stratosphere began to be investigated in the 1970's.  At first, it was thought that fleets of supersonic transport planes (SST's) would introduce water vapor and nitrous oxides into the stratosphere, degrading the atmosphere.  Fleets of these aircraft have not materialized 21

22. Anthropogenic Ozone Depletion – The Real Threat In 1974, another threat was recognized. This threat was the use of chlorofluoro-carbons (CFC's) That threat was first proposed by Molina and Rowland in 1974 As previously discussed, from 1977 to 1984 the ozone levels over Halley Bay, Antarctica decreased by 40% in the region from 12 to 24 kilometers 22

23. 23 Nobel Prize in Chemistry, 1995 Left to right, Mario J. Molina, F. Sherwood Rowland, and Paul J. Crutzen

24. Antarctic Ozone Hole Development In the Antarctic the ozone hole typically begins developing in August, reaches a maximum in early October, and disappears by early December The cause of this ozone depletion has been attributed to several anthropogenic causes. 24

25. Proposed Causes Combustion products from high-flying military and civilian aircraft, particularly supersonic aircraft Nitrous oxides released from nitrogenous fertilizers Chlorofluorocarbons (CFC's), first introduced in the late 1920's, are used as refrigerants, in the manufacture of foam fast-food containers, as cleansers for electronic parts, and as propellants in aerosol cans Other compounds, such as Halon and methyl bromide, which contain bromide, and which are capable or releasing substances capable of destroying ozone. 25

26. 26 Common CFC’S Normal Designation, Formula Chemical name Other name CFC-11, Freon 11 CFCl 3 Trichlorofluoromethane CFC-12, Freon 12 CF 2 Cl 2 Dichloro-difluoromethane CFC-13, Freon 13 CF 3 ClChloro-trifluoromethane CFC-113 C 2 F 3 Cl 3 Trichloro-trifluoroethane CFC-114 C 2 F 4 Cl 2 Dichloro-tetrafluoroethane CFC-115 C 2 F 5 ClChloro-pentafluoroethane HCFC-22 CHF 2 ClChloro-difluoromethane HCFC-123 CHCl 2 CF 3 Dichloro-trifluoroethane HCFC-124 CHFClCF 3 Chloro-trifluoroethane HFC-125 CHF 2 CF 3 Pentafluoroethane HCFC-132b C 2 H 2 F 2 Cl 2 Dichloro-difluoroethane HFC-134a CH 2 FCF 3 Tetrafluoroethane HCFC-141b CH 3 CFCl 2 Dichlorofluoroethane HCFC-142b CH 3 CF 2 Cl Chloro-difluoroethane HFC-143a CH 3 CF 3 Trifluoroethane HFC-152a CH 3 CHF 2 Difluoroethane HALON 1211 CF 2 BrClBromochloro-ifluoromethane HALON 1301 CF 3 BrBromo-trifluoroethane HALON 2402 C 2 F 4 Br 2 Dibromo-tetrafluoroethane After Houghton et al., 1990, Appendix 8

27. 27 Relative bond strengths BondBond Strength, kcal/mole C-H 80.9 C-Br 95.6 C-F107 Data from Weast, 1966

28. Rowland’s Nobel Prize Lecture “When Mario Molina joined my research group as a postdoctoral research associate later in 1973, he elected the chlorofluorocarbon problem among several offered to him, and we began the scientific search for the ultimate fate of such molecules. At the time, neither of us had any significant experience in treating chemical problems of the atmosphere, and each of us was now operating well away from our previous areas of expertise. 28

29. Rowland’s Lecture - 2 The search for any removal process which might affect CCl 3 F began with the reactions which normally affect molecules released to the atmosphere at the surface of the Earth. Several well-established tropospheric sinks - chemical or physical removal processes in the lower atmosphere - exist for most molecules released at ground level: 29

30. Rowland’s Lecture - 3 1. Colored species such as the green molecular chlorine, Cl 2, absorb visible solar radiation, and break apart, or photodissociate, into individual atoms as the consequence; 2. Highly polar molecules, such as hydrogen chloride, HCl, dissolve in raindrops to form hydrochloric acid, and are removed when the drops actually fall; and 30

31. Rowland’s Lecture - 4 3. Almost all compounds containing carbon-hydrogen bonds, for example CH 3 Cl, are oxidized in our oxygen-rich atmosphere, often by hydroxyl radical as in reaction (1). CH 3 Cl + HO → H 2 O + CH 2 Cl (1) 31

32. Rowland’s Lecture - 5 However, CCl 3 F and the other chlorofluorocarbons such as CCl 2 F 2 and CCl 2 FCClF 2 are transparent to visible solar radiation and those wavelengths or ultraviolet (UV) radiation which penetrate to the lower atmosphere, are basically insoluble in water, and do not react with HO, O 2, O 3, or other oxidizing agents in the lower atmosphere. When all of these usual decomposition routes are closed, what happens to such survivor molecules?” 32

33. Stability of CFC’s CFC stability was at first thought to make them an ideal industrial compounds because they are unreactive and therefore nontoxic Carbon-chlorine bonds can be broken by ultraviolet radiation, releasing chlorine free radicals 33

34. 34 Destruction of Ozone

35. 35 Freon 11 Levels

36. 36 Freon 12 Levels

37. HCFC trends HCFC-22, HCFC-141b HCFC-142b 37

38. 38 Halon Compounds Halon-1211 Halon-1301 Methyl bromide Halons are used primarily as fire retardants Methyl bromide was used as a soil fumigant

39. CFC Control 1978 – U.S. ban on use in hair sprays and deodorants 1987 – Montreal Protocol 2005 – Methyl bromide phaseout in U.S. completed 39

40. Chlorine Loading 40

41. 41 Chlorine Destruction Mechanisms

42. Nitrogen Gases Nitrogen gases attack ozone approximately as follows  Nitrous oxide (N 2 O) is produced as a by-product of nitrification and denitrification in soils and oceans  In the troposphere, there are no known degradation reactions for nitrous oxide, so it migrates upward into the stratosphere  Most of the nitrous oxide will be destroyed by photodissociation into oxygen atoms and N 2  Approximately 10% escapes this fate and is destroyed by reaction with activated atomic oxygen 42

43. 43 Nitrogen Oxide Reactions

44. Computer Model Error The presence of the inhibitor reactions led the computer models to predict that CFC's should have had little effect on the ozone layer by the late 1980's Yet the ozone hole over Antarctica was unmistakably present, so something was wrong 44

45. Antarctica Antarctica is different from the temperate parts of the globe in many ways One important way is the presence of polar stratospheric clouds, or PSC's These clouds form during the Antarctica winter, when the absence of the sun for long periods lets the stratospheric temperatures dip below -78 ̊ C (<195 Kelvins) 45

46. 46 Temperatures Over the Neumayer Station

47. 47 Nacreous Clouds

48. From Laura Candler (photographer): “On January 11, 2010, a beautiful group of nacreous clouds appeared over Kiruna, Sweden. Also known as mother-of-pearl clouds, nacreous clouds sometimes form in the polar stratosphere in wintertime and glow with a silky iridescence as they undulate across the sky. I created this time lapse using images shot at 10 second intervals over the course of about 2 hours, from 10:25 a.m. until 12:14 p.m.. The images have not been manipulated in any way to enhance color, exposure, etc.” 48

49. 49 Type I Stratospheric Clouds

50. SAM II, Aboard NIMBUS 7, 1978-1993 SAM II provided vertical profiles of aerosol in both the Arctic and Antarctic polar regions SAM II was designed to develop a stratospheric aerosol database for the polar regions, allowing studies of aerosol changes due to seasonal and short-term meteorological variations, atmospheric chemistry, cloud microphysics, volcanic activity and other disruptions 50

51. Ice Particles Ice particles also serve as catalysts for the destruction of chlorine reservoir molecules Laboratory studies showed that a reaction between hydrochloric acid and chlorine nitrate (HCl and ClONO 2 ) produces photolytically unstable species such as Cl 2, ClNO 2, or HOCl on the surface of ice crystals Sunlight transforms these species into the ozone- reactive species Cl or ClO 51

52. Nacreous vs. Lenticular Clouds Nacreous clouds look like lenticular clouds which form in mountainous regions However, lenticular clouds form in the troposphere In the stratosphere, the relative humidity is about 1%, and the average water vapor content is a few parts per million It is difficult to imagine ice clouds forming under these conditions 52

53. 53 Chlorine Nitrate Reaction

54. Type III PSC’s Type III polar stratospheric clouds are similar to the nacreous clouds, except that the particle size is much larger, about ten microns Temperature must drop slowly below 190K Water ice begins to form on seed particles, either nitric acid particles or any remaining sulfuric acid aerosol Cooling is slow and the particles can grow to large size 54

55. 55 Bromine Reactions

56. Antarctic vs. Arctic Data from a major study in 1986 at McMurdo Sound, Antarctica, and other work indicate that the springtime levels of chlorine monoxide are elevated over Antarctica relative to mid-latitude stratospheric sites, and that nitrous oxide levels are severely depressed Also, both chlorine nitrate and hydrochloric acid levels are low simultaneously Work in the Arctic during the winter of 1991-92 showed that the levels of ClO increase in December, when the stratosphere first gets cold enough for PSC’s to form. 56

57. Reactions Outside Polar Vortices HCl molecules have been expected to be the major component of inorganic chlorine in the atmosphere Normally, HCl is expected to be very stable and inactive Reactions between HCl and ClNO 3 have been shown to occur rapidly on PSC-like laboratory surfaces HCl values do indeed decrease in the PSC’s However, measurements of HCl outside polar vertices also showed that HCl was sometimes lower than predicted. 57

58. Mt. Pinatubo Eruption, 1991 Substantial increase in global aerosol loading The spreading volcanic cloud reached a maximum enhancement in particle surface area of thirty times that observed during AASE I in 1989 Airborne instruments can sample and analyze changes in aerosol size and surface area along with monitoring changes in chemistry It was found that a “footprint” of heterogeneous reactions on ClO existed despite the absence of any polar stratospheric clouds in some areas Similar reductions were found in nitrogen oxides If temperatures are cold enough, the reactions on sulfate aerosol can be as efficient as those within PSC’s 58

59. Measuring Ozone A Dobson unit (DU) is the standard method of measuring ozone levels The Dobson unit is 0.01mm, or 10 microns For ozone, the Dobson units represent the thickness of the layer of ozone above a given point if all of the ozone could be brought together at a standard pressure and temperature. 59

60. Atmospheric Circulation and Ozone Distribution There is circulation at all levels of the atmosphere This circulation helps to keep the temperature of the earth more uniform than solar heating levels would otherwise suggest In the stratosphere, ozone is produced most strongly at high altitudes and low latitudes, leading to an expectation that the greatest concentrations of ozone would be found above the equator at the top of the stratosphere Actually, the ozone levels peak in the mid-stratosphere and near the poles 60

61. Antarctic Polar Vortex In the polar vortex above Antarctica the ozone levels once were about 300 Dobson units during the winter and early spring The amount would increase to about 400 Dobson units in the late spring when the polar vortex broke down, allowing exchange with mid-latitude air masses Now the ozone levels are steady throughout the winter but fall rapidly in the spring to less than 200 Dobson units The early winter ozone minimum is a natural phenomenon 61

62. Ozone Hole It is the depletion below 300 Dobson units that represents the ozone hole In 1991 the minimum low value of ozone first fell below 100 DU, to 94DU It has subsequentially fallen below 100 DU in ten additional years, with 1994 holding the record low value of 73 DU 62

63. 63 Ozone Depletion Over South Pole, 1994 and 2015

64. Current 64