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. Frith1

University College Dublin, Sept. 21, 2006

IntroductionOzone Hole trends CCM model prediction of ozone hole

Parametric modelControlling factorsModel outline

Predictions of RecoveryEstimating recoveryUncertaintiesClimate Change and Recovery

Summary

1NASA/GSFC, 2NOAA/ESRL, 3NCAR

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Introduction

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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

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Ozone Hole Trends

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TOMS 1984

SouthAmerica

Antarctica

Green-blue indicates low ozone values, while orange-red indicated high values

High values are normally found in the mid-latitudes

Extremely low values

Extremely cold temperatures are found in the lower stratosphere in spring and fall

Strong jet stream (the polar vortex) acts to confine ozone losses over Antarctica

October 1984 TOMS total ozone

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October Average Ozone HoleOctober Average Ozone Hole

LowOzone

HighOzone

Halley Bay Station

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October Antarctic Ozone

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ozonewatch.gsfc.nasa.gov

QuickTime™ and aH.264 decompressor

are needed to see this picture.

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Defining the Hole

Antarctic Ozone Hole on Oct. 4, 1998

• 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

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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

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Seasonal Ozone Hole Area

1980 1985 1990 1995 2000 20050

5

10

15

20

25

30

Antarctica area

N. America area

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Current Conditions

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Sept. 17, 2006

Aura OMIOzone < 220 DU

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Assessment of the ozone hole’s recovery (WMO, 2003)

Chapter 3 - Polar Ozone

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Model area estimates

WMO Fig. 3-47

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Model area estimates

WMO Fig. 3-47

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Model area estimates

WMO Fig. 3-47

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Minimum Ozone

WMO Fig. 3-47

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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.

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What controls Antarctic ozone

losses?

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PSCs

1. 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 K2. PSCs control de-nitrification and de-

hydration, which influences ozone loss

1. 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 K2. PSCs control de-nitrification and de-

hydration, which influences ozone lossPhoto: Paul A. Newman - Jan. 14, 2003 - Southern Scandanavia

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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

ClONO2 HNO3

Cl2

Cl2 is easily photolyzed by UV & blue/green lightHNO3 is sequestered on PSC

Antarctic ozone hole theory

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Polar Ozone Destruction

Only visible light (blue/green) needed for photolyzing ClOOClNo oxygen atoms required

Net: 2O3 + h 3O2

2 O3

3. ClOOCl+h2 Cl+O2

3 O2

1. O3 + Cl ClO + O2

2. 2 ClO + M ClOOCl + M

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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

Latitude (˚S)

Ozo

ne

(pp

mv

)

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Ozone Hole Area Versus Year

Polar vortex ≈ 33 Million km2

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Ozone Hole Residual Area Vs. T

O3 residual area: 9/21-9/30T: 9/11 - 9/20, 50 hPa, 55-75ºS

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

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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?

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Chlorine over Antarctica

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16%

32%

23%

12%

7%5%

1%4%

0

3400

3000

2000

1000

(CH3CCl3)

(e.g., HCFC-22 = CHClF2)

(CCl2FCClF2)

Naturalsources

Other gasesMethyl chloroform

HCFCs

CFC-113

Carbon tetrachloride (CCl4)

CFC-11 (CCl3F)

CFC-12 (CCl2F2)

Methyl chloride (CH3Cl)

0

20

15

10

5

15%

27-42%

5-20%20%

14%

4%

Methyl bromide (CH3Br)

Halon-1211 (CBrCIF 2)

Halon-1301 (CBrF3)

Other halons

Very-short lived gases (e.g., bromoform = CHBr3)

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

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Atmospheric Chlorine Trends from NOAA/ERL - Climate Monitoring Division

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).

50 years

102 years

5 years

42 years85 years

Steady g

rowth of

CFCs up

to 1992

CFC-11

CH3CCl3

CCl4

CFC-113

CFC-12

Production fully banned in US by

Pres. Bush

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CFC-12 released in troposphere

Carried into stratosphere in the tropics by slow

rising circulation

CFC-12 photolyzed in stratosphere by solar UV,

releasing Cl

Cl catalytically destroys O3

Cl reacts with CH4 or NO2 to form HCl or ClONO2

HCl and ClONO2 react on the

surfaces of PSCs

CFC-12 (CCl2F2) pathway to Antarctica

-90 -60 -30 0 30 60 90Latitude

1000

100

10

1

0.1

0.01P

ress

ure

(hP

a)

16

Alt

itu

de

(k

m)

0

32

48

64

80

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Mean Age-of-air

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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 windGrey lines schematically show mean flow.

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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”

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Age Spectra

The spectrum is convolved with the surface observation time series to yield the stratospheric time series.

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Fractional Release

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CCM mean age-of-air (Sept.)

CF

C-1

1

Ino

rgan

ic

0-year

CF

C-1

1

Ino

rgan

ic

1-year

CF

C-1

1

Ino

rgan

ic

2-year

CF

C-1

1

Ino

rgan

ic

3-year

CF

C-1

1

Ino

rgan

ic

4-year

CF

C-1

1

Ino

rgan

ic

5-year

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CCM mean age-of-air (Sept.)

CF

C-1

1

Ino

rgan

ic

0-year

CF

C-1

1

Ino

rgan

ic

5-year

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

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CFC-11 break down

Schauffler et al. (2003)

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Estimating chlorine over Antarctica

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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) ni f ii Cl containinghalocarbons

ni f iiBr containinghalocarbons

n = # Cl or Br atoms, f = release rate, = chemical mixing ratio, = scaling factor to account for Br efficiency for ozone loss

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EESC

Observed total chlorine* (surface)

Estimated stratospheric chlorine

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Parametric model of the ozone hole

Methodfit ozone hole size to quadratic functions of EESC and temperature

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Ozone Hole Parametric Model

EESCmax = 3.642 ppbva0 = -69.5 million km2

a1 = 50.9 million km2/ppbva2 = -1.08 million km2/KA = 0 for EESC = 1.817 ppbv = residual arear = 0.971 (r2=.943)

Area a0 a1(EESC EESC 2

2EESCmax

) a2(T Tavg ) a3(T Tavg )2

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)

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Recovery Predictions

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Ozone Hole Area vs. Year (1)

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Ozone Hole Area vs. Year (2)

Temperature effect is removed

Area a2(T Tavg ) a3(T Tavg )2

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Ozone Hole Area vs. Year (3)

Black line represents the fit of area to EESC

Area residual = 1.8 M km2

a1(EESC EESC2

2EESCmax

)

(92)

Unexplained residual for 1992 ~ 3 m km2

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Ozone Hole Area vs. Year (4)

Using WMO (2003) Cly and Bry projections, we use our fit to project the ozone hole area

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Ozone Hole Area vs. Year (5)

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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

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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

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Uncertainties

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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?

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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

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Climate change effect on ozone hole

recovery

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How will climate change impact the ozone hole?

-0.25 K/decade coolingCMIP2 data from IPCC (2001)

• 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

No trend

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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

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END

Jan. 10, 2003 - local noon, Kiruna, SwedenJan. 10, 2003 - local noon, Kiruna, Sweden