1
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
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 mankind’s ability to alter
our atmosphere and climate - forming
a useful example on climate change
policy
4
Ozone Hole Trends
5
TOMS 1984
Extremely cold temperatures
are found in the lower
stratosphere in spring and
fall
South
America
Extremely low
values
Green-blue
indicates low
ozone values,
while orange-red
indicated high
values
Antarctica
Strong jet stream
(the polar vortex)
acts to confine ozone
losses over
Antarctica
High values are normally found in the mid-latitudes
October 1984 TOMS total ozone
6
October Average Ozone Hole
Halley Bay Station
Low
Ozone
High
Ozone
7
October Antarctic Ozone
ozonewatch.gsfc.nasa.gov
QuickTime™ and a
H.264 decompressor
are needed to see this picture.
8
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 doesn’t 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
30
25
N. America area
20
15
Antarctica area
10
5
0
1980
1985
1990
1995
2000
2005
12
Current Conditions
13
Sept. 17, 2006
Ozone < 220 DU
Aura OMI
15
Assessment of the ozone
hole’s 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
1.
2.
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
HCl
Cl2
ClONO2
HNO3
Cl2 is easily photolyzed by UV & blue/green light
HNO3 is sequestered on PSC
24
Polar Ozone Destruction
1. O3 + Cl  ClO + O2
3. ClOOCl+h2 Cl+O2
2 O3
3 O2
2. 2 ClO + M  ClOOCl + M
Only visible light (blue/green) needed for photolyzing ClOOCl
No oxygen atoms required
Net: 2O3 + h  3O2
25
Chlorine and Bromine
Ozone (ppmv)
NOZE 1 & 2 missions in 1986: Highconcentrations 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
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
hole’s area will be 1.1 Million km2 larger than normal.
See Newman and Nash, GRL, 2004 O residual area: 9/21-9/30
3
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
1%
4%
5%
7%
3400
3000
Other gases
Methyl chlor oform (CH3CCl3)
HCFCs (e.g., HCFC-22 = CHClF2)
CFC-113 (CCl2FCClF2)
Other halons
20
Carbon tetrachloride
(CCl4)
12%
14%
Halon-1301 (CBrF 3)
Halon-1211 (CBrCIF 2)
15
CFC-11 (CCl3F)
20%
5-20%
2000
23%
4%
Methyl bromide (CH 3Br)
10
CFC-12 (CCl2F2)
1000
5
32%
0
Natural
sources
16%
27-42%
Methyl chloride (CH3Cl)
0
Very-short lived gases
(e.g., bromoform = CHBr 3)
15%
• 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
Atmospheric Chlorine Trends from
NOAA/ERL - Climate Monitoring Division
31
102 years
CFC-12
CFC-11
50 years
CH3CCl3
CFC-113
Production fully
banned in US by
Pres.CCl
Bush
4
42 years
85 years
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
48
2
Carried into stratosphere
the tropics by slow
HCl and ClONO2 in rising
circulation
react on the
surfaces
of PSCs
16
0.1
1
10
32
Pressure (hPa)
Altitude (km)
64
Cl catalytically
destroys O3
photolyzed in
Cl reacts with CH4CFC-12
or
by solar UV,
NO2 to form HClstratosphere
or
releasing Cl
ClONO
100
CFC-12 released in troposphere
0
-90
-60
-30
0
Latitude
30
60
1000
90
33
Mean Age-of-air
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.
34
CCM mean age-of-air (Sept.)
35
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.)
4-year
3-year
CFC-11
CFC-11
Inorganic
Inorganic
Inorganic
2-year
CFC-11
Inorganic
Inorganic
Inorganic
0-year
CFC-11
1-year
CFC-11
CFC-11
5-year
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
Inorganic
0-year
Inorganic
CFC-11
CFC-11
5-year
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
EESC(t) 
 n f    n f 
i i
Clcontaining
halocarbons
i
i i
Brcontaining
halocarbons
i
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
EESC 2
2
Area  a0  a1(EESC 
)  a2 (T  Tavg )  a3 (T  Tavg )  
2EESCmax
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)
Area  a2 (T  Tavg )  a3 (T  Tavg )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
EESC 2
a1 (EESC 
)
2EESCmax

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 sensitivity=9.0 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