Is the Ozone Layer Recovering

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Is the Ozone Layer Recovering?

• Dr. Paul A. Newman
• http//code613-3.gsfc.nasa.gov/People/Newman/
• NASAs Goddard Space Flight Center
• Global Climate Change Forum
• The Field Museum, Chicago, Ill.
• March 25, 2006

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Outline

• Introduction
• Whats the problem?
• Some basic facts about ozone
• What are the gases that cause ozone loss?
• How does the ozone hole form?
• What do the latest ozone trends look like?
• Predictions - Wheres ozone headed?
• Summary

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Science begins with quality measurements (numbers)
Aurora over Halley Bay Station, Antarctica,
75.6ºS 26.5ºE Brunt Ice Shelf, Coats Land 105
days of continuous darkness, twice per year
re-supply Population 65 in summer, 15 in winter
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Farman, Gardiner, Shanklin (1985)
Farman et al. (Nature, 1985)
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What is ozone?
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Ozone Basic Facts
O3 Ozone is composed of 3 oxygen atoms. O3
inhalation becomes a problem at concentrations
greater than 80 parts per billion sustained
during a continuous 8-hour period (EPA). O3
absorbs harmful solar ultraviolet radiation. A
necessary condition for life. O3 is mainly found
in the the stratosphere. O3 both heats the
stratosphere by absorbing UV and is a greenhouse
gas (absorbing and emmiting in the Infrared). O3
concentrations are small (peak concentrations are
about 10 parts per million at an altitude of
about 32 km (20 miles). Mass (Billion Metric
Tons) Sun 1,9900,000,000,000,000,000 Earth 5,9
80,000,000,000 Global atmosphere 5,300,000 Global
ozone 3
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Atmospheric Structure
100
60
Thermosphere
80
50
Mesosphere
40
60
Altitude (miles)
Altitude (km)
30
40
20
20
10
Troposphere
0
0
0
2
4
6
8
Ozone (parts per million)
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Ozone Facts
100
60
Thermosphere
80
50
Mesosphere
40
60
Altitude (miles)
Altitude (km)
30
40
90 of ozone is in the stratosphere
20
20
10
10 of ozone is in the troposphere
Troposphere
0
0
0
2
4
6
8
Ozone (parts per million)
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What does ozone do?
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Ozone Facts
Ozone is the Earths natural sunscreen
100
60
Thermosphere
80
50
UVc - 100 Absorption
Mesosphere
UVb - 90 Absorption
40
UVa - 50 Absorption Scattering
60
Altitude (miles)
Altitude (km)
30
40
20
20
10
Troposphere
0
0
0
2
4
6
8
Ozone (parts per million)
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Health Facts

• UV plusses produces vitamin D in the skin -
  necessary to maintain levels of calcium and
  phosphorus (10-15 minutes twice a week)
• UV minuses
• Eye damage cataracts, photokerititus
  (snowblinding), ocular cancers
• Skin cancers basal, squamous, melanoma
• photoaging
• Damage to various land species
• Damage to aquatic species
• Increased pollution levels in urban environments
• Tropospheric ozone is a pollutant aggravates
  asthma, reduces lung capacity, and increases
  susceptibility to respiratory illnesses like
  pneumonia and bronchitis

Cataract
Melanoma
Mexico City
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Future cancer rate projections
Cases in excess of 1980 levels ( 2000 per
million) Without the protocol, excess cases would
have increase unchecked
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What chemicals cause ozone loss?
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Source Chemicals

• Cl is much more abundant than Br
• Br is about 50 times more effective at O3
  destruction

From Ozone FAQ - see http//www.unep.org/ozone/faq
.shtml
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Atmospheric Chlorine Trends from NOAA/ERL -
Climate Monitoring Division
102 years
CFC-12
CFC-11
Steady growth of CFCs up to 1992
50 years
CH3CCl3
CCl4
42 years
85 years
CFC-113
5 years
Updated Figure made by Dr. James Elkins from
Trends of the Commonly Used Halons Below
Published by Butler et al. 1998, All CFC-113
from Steve Montzka (flasks by GC/MS), and recent
updates of all other gases from Geoff Dutton (in
situ GC).
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Global Stratospheric Chlorine trends
Time evolution of chlorine From WMO (2003) -
Figure 1-7
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What causes the ozone hole?
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How does chlorine get from our refrigerators to
the Antarctic stratosphere?
Cl catalytically destroys O3
Cl reacts with CH4 or NO2 to form non-reactive
HCl or ClONO2
CFC-12 photolyzed in stratosphere by solar UV,
releasing Cl
Cl released by PSCs
Carried into stratosphere in the tropics by slow
rising circulation
CFC-12 released in troposphere
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Polar Stratospheric Clouds
Central, Sweden January 14, 2003 - P. Newman
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Antarctic ozone hole theory
Solomon et al. (1986), Wofsy and McElroy (1986),
and Crutzen and Arnold (1986) suggest reactions
on cloud particle surfaces as mechanism for
activating Chlorine
Cl2 is easily photolyzed by UV blue/green
light HNO3 is sequestered on PSC
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Polar Ozone Destruction
1. O3 Cl ? ClO O2
3. ClOOClh??2 ClO2
3 O2
2 O3
2. 2 ClO M ? ClOOCl M
Only visible light (blue/green) needed for
photolyzing ClOOCl No oxygen atoms required Net
2?O3 solar photon ? 3?O2
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Ozone Hole timeline
May
Jun
Jul
Aug
Sep
Oct
Nov
Temp
? Polar night falls and temp cool
? Sunlight induces catalytic O3 loss
? PSCs begin to form
? Chlorine is freed into reactive forms
T become too warm for PSCs, O3 loss stops ?
Ozone hole breaks-up, mixes low ozone across SH ?
Ozone
Cold T ? PSCs high Cly ? het reactions ? Large
catalytic loss
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Whats the latest on ozone trends?
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October Antarctic Ozone
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October Average Ozone Hole
Low Ozone
High Ozone
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Arctic Antarctic Trends

• Substantial losses have occurred in the Arctic
• Arctic levels are naturally higher because of the
  structure of the NH

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Newchurch et al. (2003)

• 35-45 km, 30-50N ozone
• Note that the later year (post 1997) are above
  the downward slope
• Ozone is no longer decreasing (1st step in the
  recovery process)

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Wheres the ozone hole headed?
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Model size estimates
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Ozone Hole Area
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Ozone and climate change

• Ozone change is not a primary cause of climate
  change.
• Ozone depleting substances contribute to climate
  change.
• Ozone changes causes a climate response that is
  generally larger than the Halocarbon response.
• Climate change may seriously impact ozone levels.

See Climate Change 2001 The Scientific Basis
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Summary

• Ozone is the critical gas for screening solar UV
  radiation. Quality, long-term observations are
  critical for assessing change!
• Ozone loss resulted from human produced ozone
  destroying substances (ODS CFCs and halons).
  These chemicals have extremely long lifetimes.
• ODSs have been regulated under international
  agreements and are slowly decreasing.
• Ozone levels are not getting worse, but we cant
  say that things are getting better (yet).
• The ozone hole will recover by about 2068.
• Every year of delay in regulating ozone would
  have resulted in a 9 year delay of recovery.
• The impact of climate change on ozone recovery is
  very uncertain at present.