Ozone Layer: Existence and Anthropogenic Depletion

1. Ozone Layer: Existence and Anthropogenic Depletion GLY 4241 - Lecture 7 Fall, 2014

2. Atmospheric Layers

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

4. Ultraviolet Radiation

5. Absorption of Solar Radiation

6. Effects of Increased UV • Modify rate of photosynthesis • Marine phytoplankton • Terrestrial crop and plant damage • Leads to increased CO2 levels in the atmosphere • Species specific effects – diatoms vs. phaeocystis

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. 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

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

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-1photosynthetic active radiation with different daily UV-B doses. • f, UV-B1 2.3 kJ/m2d • g, UV-B2 6.6 kJ/m2d • h, UV-B3 18.6 kJ/m2d • i, UV-B4 27.1 kJ/m2d • 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

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

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

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. 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.

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

20. 2013 Ozone Hole

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.

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

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.

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.

26. CommonCFC’S • Normal Designation, Formula Chemical name Other name • CFC-11, Freon 11 CFCl3 Trichlorofluoromethane • CFC-12, Freon 12 CF2Cl2 Dichloro-difluoromethane • CFC-13, Freon 13 CF3Cl Chloro-trifluoromethane • CFC-113 C2F3Cl3 Trichloro-trifluoroethane • CFC-114 C2F4Cl2 Dichloro-tetrafluoroethane • CFC-115 C2F5Cl Chloro-pentafluoroethane • HCFC-22 CHF2Cl Chloro-difluoromethane • HCFC-123 CHCl2CF3 Dichloro-trifluoroethane • HCFC-124 CHFClCF3 Chloro-trifluoroethane • HFC-125 CHF2CF3 Pentafluoroethane • HCFC-132b C2H2F2Cl2 Dichloro-difluoroethane • HFC-134a CH2FCF3 Tetrafluoroethane • HCFC-141b CH3CFCl2 Dichlorofluoroethane • HCFC-142b CH3CF2Cl Chloro-difluoroethane • HFC-143a CH3CF3 Trifluoroethane • HFC-152a CH3CHF2 Difluoroethane • HALON 1211 CF2BrCl Bromochloro-ifluoromethane • HALON 1301 CF3Br Bromo-trifluoroethane • HALON 2402 C2F4Br2 Dibromo-tetrafluoroethane After Houghton et al., 1990, Appendix 8

27. Relative bond strengths 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.

29. Rowland’s Lecture - 2 • The search for any removal process which might affect CCl3F 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:

30. Rowland’s Lecture - 3 • 1. Colored species such as the green molecular chlorine, Cl2, 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

31. Rowland’s Lecture - 4 • 3. Almost all compounds containing carbon-hydrogen bonds, for example CH3Cl, are oxidized in our oxygen-rich atmosphere, often by hydroxyl radical as in reaction (1). • CH3Cl + HO → H2O + CH2Cl (1)

32. Rowland’s Lecture - 5 • However, CCl3F and the other chlorofluorocarbons such as CCl2F2 and CCl2FCClF2* 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, O2, O3, or other oxidizing agents in the lower atmosphere. When all of these usual decomposition routes are closed, what happens to such survivor molecules?”

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

34. Destruction of Ozone

35. Freon 11 Levels

36. Freon 12 Levels

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

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

40. Chlorine Loading

41. Chlorine Destruction Mechanisms

42. Nitrogen Gases • Nitrogen gases attack ozone approximately as follows • Nitrous oxide (N2O) 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 N2 • Approximately 10% escapes this fate and is destroyed by reaction with activated atomic oxygen

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

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 -78̊C (<195 Kelvins)

46. Temperatures Over the Neumayer Station

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.”

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