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A.R. (Ravi) Ravishankara NOAA, ESRL/Chemical Sciences Division Boulder CO, USA Co-Chair, SAP PowerPoint Presentation
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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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slide1

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

ozone depletion and cfcs pre ozone hole
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

the predicted ozone depletion

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”

slide6

The Antarctic ozone hole was very large!

Depletions of 30%

Larger than many large countries!

many theories of ozone hole
Many theories of ozone hole

Ozone depletion due to:

Super human causes

  • Natural causes
    • Dynamical reasons
    • Cosmic rays
  • Human caused
  • - CFCs (+ other halogens)
slide8

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

slide9

Expedition to McMurdo station in 1986 clearly implicated chlorine from CFCs and indicated that other theories were unlikely to be correct

Courtesy: Dr. Solomon

slide10

40

Altitude (km)

20

0

Amount of ozone

complex new chemistry quantified
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

reactions with high chlorine quantified
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.

explanation of antarctic ozone hole the perfect storm
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
graphic realization of what can happen elsewhere
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!

slide17

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