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A.R. (Ravi) Ravishankara NOAA, ESRL/Chemical Sciences Division Boulder CO, USA Co-Chair, SAP

Explanation of the ozone hole and verification of the connections between ozone depleting substances and the ozone hole. A.R. (Ravi) Ravishankara NOAA, ESRL/Chemical Sciences Division Boulder CO, USA Co-Chair, SAP. Some personal reflections

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A.R. (Ravi) Ravishankara NOAA, ESRL/Chemical Sciences Division Boulder CO, USA Co-Chair, SAP

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  1. Explanation of the ozone hole and verification of the connections between ozone depleting substances and the ozone hole A.R. (Ravi) Ravishankara NOAA, ESRL/Chemical Sciences Division Boulder CO, USA Co-Chair, SAP Some personal reflections Many simplifications for the sake brevity and clarity

  2. Ozone Depletion and CFCs: Pre-ozone hole Rowland and Molina theory of ozone depletion- mid 1970s. Work done in the laboratory, atmospheric, and modeling to estimated future ozone depletion Most chlorine from CFCs are in the “benign” (non-ozone-destruction) chemical forms. Chlorine nitrate and Hydrogen chloride Ozone destroying fraction (chlorine atoms) is usually only about 1% of total! Not much ozone loss in the region of most ozone. Main pathway: Ozone destruction here Cl atoms: Catalysts for ozone destruction CFCs released at Earth’s surface

  3. ClONO2 NAS Reports 1976 The “predicted” ozone depletion CFC induced depletion predicted for ~2050; chlorine levels of ~9.5 ppbv Coupling of ozone depletion due to Chlorine (CFCs) and nitrogen oxides (SSTs) NOx emissions could enhance, instead of depleting, ozone Predicted ozone depletion- in the future and “modest”

  4. Thanks to Dr. Solomon for this slide The Ozone Hole

  5. The Antarctic ozone hole was very large! Depletions of 30% Larger than many large countries!

  6. Many theories of ozone hole Ozone depletion due to: Super human causes • Natural causes • Dynamical reasons • Cosmic rays • Human caused • - CFCs (+ other halogens)

  7. Gases destroy ozone here 40 Polar cloud surfaces lead to much more ozone destruction, in the heart of the layer Reservoirs HCl Altitude (km) 20 Cl2 Cl ClONO2 ClO Ozone chlorine 0 CFCs Activated for ozone loss Amount of ozone 20 On the depletion of Antarctic ozone, Nature 321, 755-758 (19 June 1986) Susan Solomon*, Rolando R. Garcia†, F. Sherwood Rowland‡ & Donald J. Wuebbles§ Courtesy of Dr. Solomon

  8. Expedition to McMurdo station in 1986 clearly implicated chlorine from CFCs and indicated that other theories were unlikely to be correct Courtesy: Dr. Solomon

  9. 40 Altitude (km) 20 0 Amount of ozone

  10. The smoking gun! 1987 Aircraft ExpeditionMeasurements right inside the ozone hole

  11. Chlorine from CFCs are responsible for ozone depletion! Pre-sunlight data is not real

  12. Complex New Chemistry Quantified Many other reactions that occur on ice and ice-like substances were elucidated and quantified Laboratory studies elucidated how particles are formed in the stratosphere. Examined reactivities on/in these particles. Atmospheric observations confirmed these particles. Figure courtesy of Dr. Margaret Tolbert Key point: Most (nearly 100%) chlorine in active ozone-destroying form! Compare this with only 1% in active form elsewhere

  13. Reactions with high chlorine quantified Ozone destruction chemistry in the ozone hole different from elsewhere in stratosphere- Very unusual chemistry First suggested as a possible reaction in the 1950s by Norrish et al. Molina et al. suggested it for the atmosphere with high chlorine Laboratory studies quantified the rates of these reactions This high-order dependence on ClO abundance accounted for rapid onset of the ozone hole.

  14. Explanation of Antarctic Ozone hole: The perfect Storm From Ravishankara, 2010 • Confluence of a large number of factors added to create ozone hole! • Unusually cold conditions allow formation of particles • The unusually atmospheric motion that “contains” air over Antarctica • Some reactions that take away the “moderating” nitrogen oxides • Light shines in to the “pre-conditioned cauldron” and destroys a lot of ozone! • Chlorine continues to destroy ozone “uncontrolled” till the vortex falls apart

  15. Graphic realization of what can happen elsewhere! The ozone hole was a graphic “poster child” for the ozone layer depletion • The global nature was evident- no CFCs emitted by Antarctica, yet a huge “hole” from contributions of others! • The “predictable” periodicity of ozone hole made it easier to diagnoze/understand • Huge increases in UV over Antarctica, levels equal to those in San Diego in the summer • Viewed as a harbinger of things to come • The “predictable” periodicity of ozone hole also was a clear recurring reminder. You all did the rest- the Montreal Protocol!

  16. Ozone layer passed from “curiosity-driven” issue to “societal issue!” Ozone hole discovered Ozone hole “explained” Ozone hole explanation “Verified” Potential human caused large ozone depletion was clear Harmful effects of enhanced UV light recognized

  17. Thank you for your attention.

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