Recovery of the Antarctic ozone hole P. Newman1, E. Nash1, S. R. Kawa1, S. Montzka2, Susan Schauffler3, R. Stolarski1, S. Pawson1, A. Douglass1, J. E. Nielsen1, S. Frith1 University College Dublin, Sept. 21, 2006

1
Recovery of the Antarctic ozone holeP. Newman1,
E. Nash1, S. R. Kawa1, S. Montzka2, Susan
Schauffler3, R. Stolarski1, S. Pawson1, A.
Douglass1, J. E. Nielsen1, S. Frith1University
College Dublin, Sept. 21, 2006
Introduction Ozone Hole trends CCM model
prediction of ozone hole Parametric
model Controlling factors Model
outline Predictions of Recovery Estimating
recovery Uncertainties Climate Change and
Recovery Summary
1NASA/GSFC, 2NOAA/ESRL, 3NCAR
2
Introduction
3
Why is understanding ozone hole recovery
important?

• The ozone hole is the poster child of atmospheric
  ozone depletion
• Scientists staked their reputations on ozone
  depletion - international regulations were
  implemented. We need to carry our predictions
  through.
• Severe ozone holes lead to acute UV events in
  mid-latitudes
• Possible regulation changes could accelerate the
  phase out of ozone depleting chemicals.
• The ozone hole is a fundamental example of
  mankinds ability to alter our atmosphere and
  climate - forming a useful example on climate
  change policy

4
Ozone Hole Trends
5
TOMS 1984
October 1984 TOMS total ozone
6
October Average Ozone Hole
Low Ozone
High Ozone
7
October Antarctic Ozone
8
ozonewatch.gsfc.nasa.gov
9
Defining the Hole

• Ozone hole area is defined by the area coverage
  of ozone values less than 220 DU 24.7 M km2
• 220 DU located near strong gradient
• 220 DU is lower than values observed prior to
  1979
• Values of 220 tend to appear in early September.
  TOMS doesnt make measurements in polar night!
• Values of 220 tend to disappear in late November
• Ozone hole minimum is 94 DU

Antarctic Ozone Hole on Oct. 4, 1998
10
Daily Ozone Hole Area
24.7 M km2 on Oct. 4, 1998
Derive average size from an average of daily
values Sep. 7-Oct. 13
11
Seasonal Ozone Hole Area
12
Current Conditions
13
Sept. 17, 2006
Ozone lt 220 DU
Aura OMI
14
Current Conditions
15
Assessment of the ozone holes recovery (WMO,
2003)
Chapter 3 - Polar Ozone
16
Model area estimates
WMO Fig. 3-47
17
Model area estimates
WMO Fig. 3-47
18
Model area estimates
WMO Fig. 3-47
19
Minimum Ozone
WMO Fig. 3-47
20
Model Predictions Summary

• WMO assessment (2004) These models suggest that
  the minimum column ozone may have already
  occurred or should occur within the next decade,
  and that recovery to 1980 levels may be expected
  in the 2045 to 2055 period.
• CCM losses tend to be too small
• All of the CCMs underestimate the ozone hole
  area.
• In general, the CCMs overestimate the depth of
  the ozone hole.

21
What controls Antarctic ozone losses?
22
PSCs

• PSC composition phase are key to heterogeneous
  reaction rates
• II - Crystaline water Ice 188 K
• Ia - Crystaline particles above frost point 195
  K
• Ib - liquid particles above the frost point 192
  K
• PSCs control de-nitrification and de-hydration,
  which influences ozone loss

Photo Paul A. Newman - Jan. 14, 2003 - Southern
Scandanavia
23
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
24
Polar Ozone Destruction
2 O3
Only visible light (blue/green) needed for
photolyzing ClOOCl No oxygen atoms required Net
2?O3 h? ? 3?O2
25
Chlorine and Bromine
NOZE 1 2 missions in 1986 High-concentrations
of chlorine monoxide at low altitudes in the
Antarctic spring stratosphere -
diurnal-variations, R. Dezafra, M. Jaramillo, A.
Parrish, P. Solomon, B. Connor, J. Barrett,
Nature, 1987 AAOE mission in August-September
1987 observations inside the polar vortex show
high ClO is related to a strong decrease of ozone
over the course of the Antarctic spring J.
Anderson et al., JGR, 1989
Ozone (ppmv)
Latitude (S)
26
Ozone Hole Area Versus Year
Polar vortex 33 Million km2
27
Ozone Hole Residual Area Vs. T
If the temperature is 1 K below normal, then
ozone holes area will be 1.1 Million km2 larger
than normal. See Newman and Nash, GRL, 2004
O3 residual area 9/21-9/30 T 9/11 - 9/20, 50
hPa, 55-75ºS
28
Problem

• We have reasonably good estimates of temperatures
  over Antarctica from radiosondes and satellite
  temperature retrievals
• We only have snapshots of Cl and Br over
  Antarctica
• How can we estimate Cl and Br over Antarctica for
  all of our observed ozone holes?

29
Chlorine over Antarctica
30
Ozone Loss Source Chemicals

• Surface concentrations 1998
• 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
31
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).
32
CFC-12 (CCl2F2) pathway to Antarctica
0.01
80
Cl catalytically destroys O3
0.1
64
CFC-12 photolyzed in stratosphere by solar UV,
releasing Cl
Cl reacts with CH4 or NO2 to form HCl or ClONO2
1
48
Altitude (km)
Pressure (hPa)
Carried into stratosphere in the tropics by slow
rising circulation
10
32
HCl and ClONO2 react on the surfaces of PSCs
100
16
CFC-12 released in troposphere
1000
0
-90
-60
-30
0
30
60
90
Latitude
33
Mean Age-of-air
34
CCM mean age-of-air (Sept.)
GSFC GEOS-4 mean age-of-air derived from advected
age tracer. Magenta line is the tropopause,
white lines are zonal mean zonal wind Grey lines
schematically show mean flow.
35
CCM mean age-of-air (Sept.)
Air at a particular point in the stratosphere is
a mixture of air parcels that have come together
from a multitude of pathways with different times
of transit. This spectrum of transit time
forms an age-spectrum that has a mean value and
a spectrum width
36
Age Spectra
The spectrum is convolved with the surface
observation time series to yield the
stratospheric time series.
37
Fractional Release
38
CCM mean age-of-air (Sept.)
39
CCM mean age-of-air (Sept.)
If we know the mean age of air (?), and we know
the fractional release rate as a function of ?,
then we can estimate the chlorine available from
CFC-11 for ozone loss
40
CFC-11 break down
Schauffler et al. (2003)
41
Estimating chlorine over Antarctica
42
Estimating halogen (Cl Br) levels over
Antarctica

• Observations show that it takes about 5.5 years
  for air to get to the Antarctic stratosphere -
  tropospheric CFCs in January 2000 yield Antarctic
  stratospheric Cl in July 2005!
• We use observed CFCs mean age-of-air estimates
  to calculate fractional release rates as a fcn.
  of age
• EESC equivalent effective stratospheric chlorine

n Cl or Br atoms, f release rate, ?
chemical mixing ratio, ? scaling factor to
account for Br efficiency for ozone loss
43
EESC
Observed total chlorine (surface)
Estimated stratospheric chlorine
44
Parametric model of the ozone hole Method?fit
ozone hole size to quadratic functions of EESC
and temperature
45
Ozone Hole Parametric Model
Area is a function of Effective Equivalent
Stratospheric chlorine (EESC) and
temperature EESC 0.8 G(CCly) G(CBry) G Age
Spectrum (6 year mean age, 3 year width) CCly and
CBry from WMO (2003)

• EESCmax 3.642 ppbv
• a0 -69.5 million km2
• a1 50.9 million km2/ppbv
• a2 -1.08 million km2/K
• A 0 for EESC 1.817 ppbv
• ? residual area
• r 0.971 (r2.943)

46
Recovery Predictions
47
Ozone Hole Area vs. Year (1)
48
Ozone Hole Area vs. Year (2)
Temperature effect is removed
49
Ozone Hole Area vs. Year (3)
?(92)
Black line represents the fit of area to
EESC Area residual ? 1.8 M km2
Unexplained residual for 1992 3 m km2
50
Ozone Hole Area vs. Year (4)
Using WMO (2003) Cly and Bry projections, we use
our fit to project the ozone hole area
51
Ozone Hole Area vs. Year (5)
52
Add uncertainty to fits

• EESC We assume mean age 5.5 years and the
  spectrum width 2.75 years EESC0
• Monte Carlo mean age (?? 0.5 years) and width
  (?? 0.5 years) to generate new EESC time series
  EESC1
• Add 80 pptv of noise to EESC1 EESC2
• Area Use original area fit (A0) added noise
  re-sampled from area residuals A1
• Refit new Area (A1) as a function of EESC2
• Project forward using EESC1 for calculating new
  recovery dates

53
Ozone Hole Area vs. Year (6)

• The ozone hole area peaked in 2001 from the area
  fit to EESC
• The ozone hole area will remain large (and
  relatively unchanged for 20 years (1997-2017)
• Area will start decreasing in approximately 2017

• The area will have decreased 1-? by 2018 and 2-?
  by 2027
• Based upon our boot-strap statistics, recovery
  will first be detected in 2024
• The area will be zero in 2070

54
Uncertainties
55
Uncertainties

• Are the chlorine and bromine levels over
  Antarctica well represented by using WMO (2003)
  and an age-spectrum for the 1979-2004 period?
• How good is WMO (2003)? New revisions (A1)
  increased recovery to 2070 from 2068.
• Is a 5.5 year mean age and a 2.75 width
  appropriate for the age spectrum?
• How do we represent interannual variability in
  age, Cly and Bry estimates?
• Will climate change impact H2O levels and the
  initial conditions for the ozone hole?

56
Full Recovery vs. mean age-of-air

• The recovery dates are proportional to our
  estimate of the mean age-of-air inside the
  Antarctic vortex Age sensitivity9.0 yr/yr
• Critical to improve our understanding of age in
  the vortex and to understand age variation in
  future climate scenarios

57
Climate change effect on ozone hole recovery
58
How will climate change impact the ozone hole?
-0.25 K/decade cooling CMIP2 data from IPCC (2001)
No trend

• Peak size 2011 (2004)
• Area will start decreasing in approximately 2018
  (2017)
• The area will have decreased 1-? by 2025 (2024)
  and 2-? by 2031 (2029)
• Based upon our boot-strap statistics, recovery
  will first be detected in 2028 (2027)
• The area will be zero in 2079 (2075)
• magenta - no T-trend

59
Summary

• The area of the ozone hole is well represented by
  T and Cl and Br - We can use this to predict
  future size and minimum values of Antarctic
  ozone.
• Based upon our parametric model
• The ozone hole will remain large for a least
  another decade with no evidence of improvement
• Actual decreases will begin in about 2017, but
  can not be detected until 2023
• The full recovery will not occur until 2070
• GHG change will have small impact on recovery
• Recovery is strongly dependent on age-of-air and
  future CFC scenarios
• Current coupled models are still inadequate for
  recovery predictions

60
END
Jan. 10, 2003 - local noon, Kiruna, Sweden