OZONE LAYER: NATURAL DEPLETION AND CURRENT STATUS

1. OZONE LAYER: NATURAL DEPLETIONAND CURRENT STATUS GLY 4241 - Lecture 8 Fall, 2014

2. Mount Pinatubo Eruption, 1991

3. 1997 Montserrat Eruption

4. Sulfur Dioxide Conversion

5. Aerosol Optical Depth Analyses • BRW is Pt. Barrow, Alaska • MLO is Mauna Loa, Hawaii

6. Pinatubo Aerosol Decay

7. Surface Catalysis

8. Brasseur and Granier Model • Two-dimensional (latitude and altitude) • Extends from pole to pole • Altitude of 0 to 85 kilometers • Included 60 chemical species in 115 reactions • Time was not included in the model. • Rather, specific situations at various times after the eruption were modeled • Using several assumptions concerning net heating in the aerosol clouds, they predicted the ozone depletion levels

9. B-G Model Predictions • Largest ozone depletions were predicted near the poles, 42% depletion near the Arctic pole during the Arctic winter, and 48% depletion near the Antarctic pole during the Antarctic winter • Mid-latitude reductions in the northern hemisphere were predicted to be 10% during the winter, and 6% during the following summer

10. TOMS Results • 1992 global average total ozone amounts were 2-3% less than in any earlier year observed by TOMS (1979 to 1991) • It has been suggested that transport-effects caused by aerosol-induced radiative heating are responsible, but this has not been proven • Wilson et al. (1993) have shown that the Mount Pinatubo eruption increased aerosol surface area concentrations by factors of 30 or more

11. 1998 Prediction • Observed (solid lines, Cape Grim data) and predicted (dashed lines, Montreal Protocol) cumulative atmospheric concentrations (ppb effective chlorine) of CFCs, chlorinated solvents, HCFCs and halons

12. 2010 Mass-Weighted Emissions • Global mass-weighted emissions expressed as megatons per year • The yellow dashed line shows HCFC emissions calculated without the provisions of the 2007 accelerated HCFC phase-out under the Montreal Protocol

13. ODP-Weighted Emissions • Global Ozone Depletion Potential-weighted emissions expressed as megatons of CFC-11-equivalent per year • The emissions of individual gases are multiplied by their respective ODPs (CFC-11 = 1) to obtain aggregate, equivalent CFC-11 emissions • Dashed line marks 1987, the year of the Montreal Protocol signing.

14. Replacement of CFC’s • HCFCs and HFCs are used to replace CFCs because their chemical resistance to breakdown is less than CFC’s • Carbon-chlorine and carbon-fluorine bonds are chemically strong, and they are not easily broken • CFCs have a long residence time in the atmosphere • Carbon-hydrogen bonds are weaker, and HCFCs have substantially shorter atmospheric residence times • HFCs are advantageous because they contain no chlorine, and thus cannot release chlorine to the stratosphere • The 196 signatory nations to the Montreal protocol have encouraged all nations to replace CFC and HCFC compounds with HFCs

15. Atmospheric Chlorine Levels • Chlorine and bromine levels are starting to decrease

16. Ozone and Climate Change • As greenhouse gases build up in the troposphere, more radiation is trapped in the troposphere, cooling the stratosphere • Cooler stratospheric conditions, for a fixed amount of chlorine and bromine, results in more ozone destruction in Antarctica

17. Efforts to Cut GHG’s • It was suggested that ozone treaty personnel take over the incineration and destruction of HFC-23, a potent greenhouse gas (GHG) • This is a breakdown product of a common Freon, HCFC-22 • United Nations and the World Bank provide funding for companies that capture and destroy HFC-23 • Funding is based on the greenhouse potential of the compound, estimated at between 11,700 to 14,800 that of carbon dioxide • The residence time of HFC-23 is 270 years

18. Global Warming Potential Emissions • Global GWP-weighted emissions expressed as gigatons of CO2-equivalent per year • Emissions of individual gases are multiplied by their respective GWPs (direct, 100-year time horizon; CO2 = 1) to obtain aggregate, equivalent CO2 emissions • Shown for reference are emissions for the range of CO2 scenarios from the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES).

19. Ozone Hole Data, 2003 - 2013

20. 2012 South Pole Ozone Update • NOAA video update dated 10-1-12

21. 2013 Southern Hemisphere Observations

22. ODGI Index • In response to amendments to the Clean Air Act in 1990, NASA and NOAA were required to monitor stratospheric ozone and ozone-depleting substances • NOAA has developed an index, the Ozone Depleting Gas Index, ODGI, in order to make data concerning the ozone layer more accessible and more easily understood by the public • The ODGI index combines data from atmospheric measurements of chemicals that contain chlorine and bromine at multiple remote surface sites across the globe.

23. Source of ODGI Data • ODGI estimates come from observations at Earth’s surface of the most abundant long-lived, chlorine and bromine containing gases regulated by the Montreal Protocol • The surface-based observations provide a measure of the total number of chlorine and bromine atoms in the atmosphere likely to reach the stratosphere and contribute to ozone depletion in the near future • Antarctic stratosphere vs. mid-latitude statrosphere

24. ECI & EECI • When the enhanced efficiency of bromine to destroy ozone compared to chlorine is also considered, this total halogen amount is called the Equivalent Chlorine (ECl) burden of the atmosphere • The Equivalent Effective Chlorine (EECl) can be derived to represent how the burden of ozone-depleting halogenated gases is changing in the mid-latitude stratosphere, based on compound-dependent degradation rates in the stratosphere, a younger mean stratospheric air age, and the enhanced efficiency for bromine to destroy ozone compared to chlorine

25. Ozone Depleting Gas Concentrations

26. ODGI

27. ECl Contributions

28. EECl Contributions

29. Stratospheric Water Vapor • Measured over Boulder, Colorado utilizing balloon-borne frost-point hygrometers

30. Water Vapor Profiles, 1981 and 2013

31. Arctic Low Ozone Areas, 1979 - 2006

32. 2003 Northern Hemisphere Observations • Anomalously high total ozone values predominated over the Arctic region • Portions of the Arctic region where average values of total ozone were greater than 45 percent higher than comparable values during the early 1980s • At the same time, total ozone values over middle latitudes had much lower than average values • Lower Stratospheric minimum temperatures rarely fell below minus 78 ̊ C, producing a weak polar vortex • Amounts of Ozone Destroying Substances (ODS) reached peak values in 1997-98, and have remained high

33. Which part of the Stratosphere? • NOAA work focuses on the lower stratosphere • Core Randall and colleagues found that strong solar storms in October 2003 indirectly affected the ozone levels in the upper stratosphere • Energetic electrons and protons were blasted into the Earth's upper atmosphere, where they boosted production of nitrogen oxides by a factor of four • Inside the polar stratospheric vortex, which was exceptionally powerful during the 2003-2004 winter transported nitrogen oxides deeper into the atmosphere • At around 40 kilometers' height, the nitrogen oxides mixed with, and attacked, the ozone layer

34. Natural vs. Anthropogenic Effects • Cora Randall said, “"No one predicted the dramatic loss of ozone in the upper stratosphere of the northern hemisphere in the spring of 2004. That we can still be surprised illustrates the difficulties in separating atmospheric effects due to natural and human-induced causes."

35. 2004 Northern Hemisphere Observations • Anomalously low total ozone values predominated over the Arctic region • From 12/04 to 2/05, large portions of the Arctic region had average values of total ozone 30 to 45% lower than comparable values during the early 1980s • Size of the Arctic area of anomalously low total ozone was among the largest of any year on record since 1979 • Lower stratospheric minimum temperatures observed in portions of the Arctic region were near record low values throughout the winter, and through February remained below minus 78 ̊ C • A very strong polar vortex was associated with the regions of dominance of low ozone in the Arctic

36. 2006 Arctic Ozone

37. 2006 Ozone vs. 1979-1986 Average

38. Will Ozone Levels Return? • “Although recent data suggest that total column ozone abundances have at least not decreased over the past eight years for most of the world, it is still uncertain whether this improvement is actually attributable to the observed decline in the amount of ozone-depleting substances in the Earth’s atmosphere. The high natural variability in ozone abundances, due in part to the solar cycle as well as changes in transport and temperature, could override the relatively small changes expected from the recent decrease in ozone-depleting substances. Whatever the benefits of the Montreal agreement, recovery of ozone is likely to occur in a different atmospheric environment, with changes expected in atmospheric transport, temperature and important trace gases. It is therefore unlikely that ozone will stabilize at levels observed before 1980, when a decline in ozone concentrations was first observed.”