OCEANS AND ATMOSPHERE FLAGSHIP

The 2014 Antarctic Ozone
Hole and Ozone Science
Summary: Final Report
Final Report
Paul Krummel, Paul Fraser and Nada Derek
Oceans and Atmosphere Flagship
June 2015
Department of the Environment


Oceans and Atmosphere Flagship
Citation
Krummel, P. B., P. J. Fraser and N. Derek, The 2014 Antarctic Ozone Hole and Ozone Science
Summary: Final Report, Report prepared for the Australian Government Department of the
Environment, CSIRO, Australia, iv, 26 pp., 2015.
Copyright
© Commonwealth Scientific and Industrial Research Organisation 2015. To the extent permitted by law, all
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Contents

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Figures

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 4


Tables

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 5


Acknowledgments
The TOMS and OMI data used in this report are provided by the TOMS ozone processing team, NASA
Goddard Space Flight Center, Atmospheric Chemistry & Dynamics Branch, Code 613.3. The OMI instrument
was developed and built by the Netherlands's Agency for Aerospace Programs (NIVR) in collaboration with
the Finnish Meteorological Institute (FMI) and NASA. The OMI science team is lead by the Royal
Netherlands Meteorological Institute (KNMI) and NASA. The MERRA heat flux and temperature images are
courtesy of NASA GSFC ( />The OMPS total column ozone data used in this report are provided by NASA's NPP Ozone Science Team at
the Goddard Space Flight Center, Atmospheric Chemistry & Dynamics Branch, Code 613.3 (see
for more details). NPP is the National Polar-orbiting Partnership
satellite (NPP) and is a partnership is between NASA, NOAA and DoD (Department of Defense), see
for more details.

The Equivalent Effective Stratospheric Chlorine (EESC) data used in this report are calculated using
observations of ozone depleting substances (ODS) from the Advanced Global Atmospheric Gases
Experiment (AGAGE). AGAGE is supported by MIT/NASA (all sites); Australian Bureau of Meteorology and
CSIRO (Cape Grim, Australia); UK Department of Energy and Climate Change (DECC) (Mace Head, Ireland);
National Oceanic and Atmospheric Administration (NOAA) (Ragged Point, Barbados); Scripps Institution of
Oceanography and NOAA (Trinidad Head, USA; Cape Matatula, American Samoa). The authors would like to
thank all the staff at the AGAGE global stations for their diligent work in collecting AGAGE ODS data
This research is carried out under contract from Australian Government Department of the Environment to
CSIRO.

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 6


1 Satellite data used in this report
Full information on the satellite instruments mentioned below can be found on the following NASA website:
/>Below is a summary of the instruments, satellite platforms and resultant data that are used in this report.

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 7


1.1

TOMS

The Total Ozone Mapping Spectrometers (TOMS) were a series of satellite borne instruments that measure
the amount of back-scattered solar UV radiation absorbed by ozone in the atmosphere; the amount of UV
absorbed is proportional to the amount of ozone present in the atmosphere. The TOMS instruments flew on
a series of satellites: Nimbus 7 (24 Oct 1978 until 6 May 1993); Meteor 3 (22 Aug 1991 until 24 Nov 1994);
and Earth Probe (2 July 1996 until 14 Dec 2005). The version of TOMS data used in this report have been
processed with the NASA TOMS Version 8 algorithm.


The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 8


1.2

OMI

Data from the Ozone Monitoring Instrument (OMI) on board the Earth Observing Satellite (EOS) Aura, that
have been processed with the NASA TOMS Version 8.5 algorithm, were utilized again in the 2014 weekly
ozone hole reports. OMI continues the NASA TOMS satellite record for total ozone and other atmospheric
parameters related to ozone chemistry and climate.
On 19 April 2012 a reprocessed version of the complete (to date) OMI Level 3 gridded data was released.
This is a result of a post-processing of the L1B data due to changed OMI row anomaly behaviour (see below)
and consequently followed by a re-processing of all the L2 and higher data. These data were reprocessed by
CSIRO, which at the time resulted in small changes in the ozone hole metrics we calculate.
In 2008, stripes of bad data began to appear in the OMI products apparently caused by a small physical
obstruction in the OMI instrument field of view and is referred to as a row anomaly. NASA scientists guess
that some of the reflective Mylar that wraps the instrument to provide thermal protection has torn and is
intruding into the field of view. On 24 January 2009 the obstruction suddenly increased and now partially
blocks an increased fraction of the field of view for certain Aura orbits and exhibits a more dynamic
behaviour than before, which led to the larger stripes of bad data in the OMI images. Since 5 July 2011, the
row anomaly that manifested itself on 24 January 2009 now affects all Aura orbits, which can be seen as
thick white stripes of bad data in the OMI total column ozone images. It is now thought that the row
anomaly problem may have started and developed gradually since as early as mid-2006. Despite various
attempts, it turned out that due to the complex nature of the row anomaly it is not possible to correct the
L1B data with sufficient accuracy (≤ 1%) for the errors caused by the row anomaly, which has ultimately
resulted in the affected data being flagged and removed from higher level data products (such as the daily
averaged global gridded level 3 data used here for the images and metrics calculations). However, once the
polar night reduces enough then this should not be an issue for determining ozone hole metrics, as there is

more overlap of the satellite passes at the polar regions which essentially ‘fills-in’ these missing data.

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 9


1.3

OMPS

OMPS (Ozone Mapping and Profiler Suite) is a new set of ozone instruments on the Suomi National Polarorbiting Partnership satellite (Suomi NPP), which was launched on 28 October 2011 and placed into a sunsynchronous orbit 824 km above the Earth ( The partnership is
between NASA, NOAA and DoD (Department of Defense), see for more details.
OMPS will continue the US program for monitoring the Earth's ozone layer using advanced hyperspectral
instruments that measure sunlight in the ultraviolet and visible, backscattered from the Earth's atmosphere,
and will contribute to observing the recovery of the ozone layer in coming years. For the 2014 ozone hole
season, we also used the OMPS total column ozone data by producing metrics from both OMI and OMPS
Level 3 global gridded daily total ozone column products from NASA, and present both sets of results for
comparison.

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 10


2 The 2014 Antarctic ozone hole

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 11


2.1

Ozone hole metrics


Figure 1 shows the Antarctic ozone hole ‘depth’, which is the daily minimum ozone (DU) observed south of
35°S throughout the season. During the development of the 2014 ozone hole, the ozone minima (from the
OMI instrument) dropped quite rapidly, reaching a record low of 127 DU on 23 August. Following this the
ozone minima rose, then dipped back to 130 DU on 26 August, before rising again to 170 DU on 29 August .
The OMPS instrument record does not show the minima on 23 August as it is was performing a calibration
on this day, and OMPS did not ‘see’ the 130 DU minima that was seen by the OMI instrument on 26 August,
the OMPS ozone minimum that was recorded for this day was 165 DU. This highlights a potential problem
with this metric during the period when the polar night has not yet disappeared, in which one or two pixels
(usually close to the polar night terminator) can sometimes record very low total column ozone values. The
polar night completely ends during the first week of October each year.
Overall, the fourth week of August saw the ozone minima being generally lower than most recent years.
However, from the beginning of September the ozone minima returned to near the long-term 1979-2013
average, which it tracked until the last days of September. On 30 September the ozone minima drop to its
lowest value for 2014 of 114 DU (the OMPS instrument recorded a low of 111 DU on this date), which was
lower than 2010, 2012 & 2013, but higher than 2009 & 2011. Following this, the ozone minima increased
again either tracking or below the long-term 1979-2013 average before recovering to above the 220 DU
threshold first on 5 December, and again for the final time on 12 December. Overall, this resulted in the
2014 ozone hole being relatively shallow; the minimum ozone level recorded in 2014 was only the 21 st
deepest hole recorded (out of 35 years of TOMS/OMI satellite data, see table1). The deepest hole ever was
in 2006 (85 DU), the second deepest in 1998 (86 DU) and the 3 rd deepest in 2000 (89 DU).

Figure 1. Ozone hole ‘depth’ (minimum ozone, DU) based on OMI & OMPS satellite data. The 2014 hole based on
OMI data is indicated by the thick black line while the light blue line indicates the 2014 hole based on OMPS data.
The holes for selected previous years 2009-2013 are indicated by the thin orange, blue, red, green and pink lines
respectively; the grey shaded area shows the 1979-2013 TOMS/OMI range and mean.

Figure 2 shows the average amount of ozone (DU) within the Antarctic ozone hole throughout the 2014
season. The minimum average ozone within the hole in 2014 was 160 DU in late September, the 16 th lowest
ever recorded, again indicating a relatively shallow ozone hole. The lowest reading was in 2000 (138 DU),
the second lowest in 2006 (144 DU) and the 3 rd lowest in 1998 (147 DU).


The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 12


Figure 2. Average amount (DU) of ozone within the Antarctic ozone hole throughout the season based on OMI &
OMPS satellite data. The 2014 hole based on OMI data is indicated by the thick black line; the light blue line
indicates the 2014 hole based on OMPS data. The holes for selected previous years 2009-2013 are indicated by the
thin orange, blue, red, green and pink lines respectively; the grey shaded area shows the 1979-2013 TOMS/OMI
range and mean.

Figure 3 shows the Antarctic ozone hole area (defined as the area within the 220 DU contour) throughout
the 2014 season. The maximum daily area of the hole (23.9 million km 2 in the first week of October) was
only the 18th largest hole, with the largest in 2000 (29.8 million km 2), the 2nd largest in 2006 (29.6 million
km2) and the 3rd largest in 2003 (28.4 million km 2). The maximum in the 15-day average ozone hole area for
2014 was 22.5 million km2, the 18th largest area ever recorded, with the largest in 2000 (28.7 million km 2).

Figure 3. Ozone hole area based on OMI & OMPS satellite data. The 2014 hole based on OMI data is indicated by the
thick black line while the light blue line indicates the 2014 hole based on OMPS data. The holes for selected
previous years 2009-2013 are indicated by the thin orange, blue, red, green and pink lines respectively; the grey
shaded area shows the 1979-2013 TOMS/OMI range and mean.

Figure 4 shows the daily (24 hour) maximum ozone deficit in the Antarctic ozone hole, which is a function of
both ozone hole depth and area. This metric is not the amount of ozone lost within the hole each day, but is
The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 13


a measure of the accumulated loss summed over the lifetime of ozone within the hole as measured each
day. The maximum daily ozone deficit in 2014 was 30.7 million tonnes (Mt) in the first week of October, the
16th largest deficit ever and falls about ‘middle of the pack’ for the 35 years of satellite records; the largest
was in 2006 (45.1 Mt).

Integrated over the whole ozone-hole season, the total ozone deficit (the sum of the daily ozone deficits)
was about 1252 Mt of ozone in 2014 (1220 Mt based on OMPS), the 18 th largest cumulative ozone deficit
ever recorded, the largest was in 2006 (2560 Mt).

Figure 4. OMI & OMPS estimated daily ozone deficit (in millions of tonnes, Mt) within the ozone hole. The 2014 hole
based on OMI data is indicated by the thick black line while the light blue line indicates the 2014 hole based on
OMPS data. The holes for selected previous years 2009-2013 are indicated by the thin orange, blue, red, green and
pink lines respectively; the grey shaded area shows the 1979-2013 TOMS/OMI range and mean. The estimated total
(integrated) ozone loss for each year is shown in the legend.

Apart from the discrepancies in the ozone column minima seen during the fourth week of August
(mentioned above), in general the ozone hole metrics presented here based on the OMI and OMPS records
compare very well, as can be seen in Figures 1-4. This is an encouraging result and gives confidence that the
OMPS instrument can seamlessly continue the long-term OMI/TOMS ozone hole records.

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 14


2.2

Total column ozone images

The daily total column ozone data over Australia and Antarctica for September, October and November
2014 from OMI are shown in Appendix A Figures A.1, A.2 and A.3 respectively; and images from OMPS for
September, October and November 2014 are shown in Appendix A Figures A.4, A.5 and A.6 respectively.
During the second week of September the 220 DU contour that defines the ozone hole completely closed.
The polar night is clearly visible in the images for September, with it successively reducing each day until it
had completely disappeared by 3 October.
The dominant feature of the daily images for 2014 was once again the ridge of high ozone immediately
south of Australia, predominantly during September and October (whole month). The ridge is particularly

evident during 12-19 September and 3-15 October, which saw extended areas in the ridge (around 60°S
latitude) with total column ozone concentrations greater than 450 DU. This resulted in the ozone hole being
displaced off the pole towards the Atlantic Ocean during these periods and at times up to a third to a half of
the Antarctic continent being outside of the ozone hole. During these periods the polar vortex (and hence
the ozone hole) became quite elongated, resulting in the tip of South America being one the edge of or
within the ozone hole on 14-17 September; 6-7 & 10 October; and 12-14 November.
Between the above mentioned periods of high ozone, the polar vortex/ozone hole was quite symmetrical,
with the three Australian Antarctic stations (Mawson, Davis & Casey) being on the edge of or completely
inside the ozone hole on 6-7 September, 20-21 September, 26-30 September and 1 October (the date of the
peak ozone hole area for 2014). There were also several periods when all of the Australian Antarctic stations
were outside of the ozone hole: 15, 22-23 September; and 16-18 October. The Australian sub-Antarctic
station at Macquarie Island spent most of the 2014 ozone hole season under the high ridge of ozone.
During the period 18-28 October the polar vortex/ozone hole was remarkably stable and mostly
symmetrical, with the ridge of high ozone south of Australia still very prominent. The polar vortex started to
become distorted again during 29-31 October, with the distortion becoming significant during 1-3
November, the result of which was a sharp reduction in ozone hole area, and a small pocket of ozone
depleted air detaching from the main ozone hole on 4 November immediately south of Australia along the
Antarctic coastline. This signalled the beginning of the breakup of the 2014 ozone hole through a series of
polar vortex distortions (8-13 November, 23-25 November) with the ozone hole progressively dropping in
area and depth before fully recovering in early December.

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 15


2.3

Antarctic meteorology/dynamics

The 2014 MERRA 45-day mean 45-75°S heat fluxes at 50 & 100 hPa are shown in the left hand panels of
Figure 5. A less negative heat flux usually results in a colder polar vortex, while a more negative heat flux

indicates heat transported towards the pole (via some meteorological disturbance/wave) and results in a
warming of the polar vortex. The corresponding 60-90°S zonal mean temperatures at 50 & 100 hPa for 2014
are shown in the right hand panels of Figure 5, these usually show an anti-correlation to the heat flux.
Up to mid-September, the heat flux at the 50 & 100 hPa levels was similar to or more negative than the
long-term average, with the corresponding temperatures at the 50 & 100 hPa level being about average.
During the third week of September a small negative heat flux event occurred and can be seen in both the
50 & 100 hPa traces, which is more pronounced in the 60-90°S zonal mean temperatures at 100 & 50 hPa
which show an increase, most noticeably at the 100 hPa level where the temperature reach the 90 th
percentile of the 1979-2013 range.
During the second, third and fourth weeks of October the 45 day mean 45-75°S heat flux at the 50 & 100
hPa levels dropped to be in the bottom 10-30% of the 1979-2013 range and remained there until lateOctober/early-November, indicating significant transport of heat towards the South Pole and hence
disturbance of the polar vortex. Correspondingly, the 60-90°S zonal mean temperature at the 50 & 100 hPa
levels increased rapidly, with the 100 hPa trace in the highest 10 th percentile for a period in mid-October.
These two warming events help explain the changes in the ozone hole metrics at the same time (as seen in
Figures 1-4), especially the ozone hole area.
Lastly, during the first week of November the 45 day mean 45-75°S heat flux at the 100 hPa level returned
to the bottom 10-30% of the 1979-2013 range and remained there until the third week of November.
However, following a brief increase in the first week on November, the 60-90 °S zonal mean temperature at
the 50 & 100 hPa levels returned to be around the 1979-2013 mean for the remainder of the year.
Correspondingly, the ozone hole metrics followed trajectories close to the long-term means during
November, with the ozone hole recovering in the first week of December.

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 16


Figure 5. NASA MERRA heat flux and temperature. The 45-day mean 45°S-75°S eddy heat flux at 50 and 100 hPa are
shown in the two left hand panels. The 60°S-90°S zonal mean temperature at 50 & 100 hPa are shown in the
right two panels. Images courtesy of NASA GSFC – />
The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 17



3 Comparison to historical metrics
Table 1 contains the ranking for all 35 ozone holes recorded since 1979 for the various metrics that measure
the ‘size’ of the Antarctic ozone hole: 1 = lowest ozone minimum, greatest area, greatest ozone loss etc.; 2 =
second largest….
The definitions of the various metrics are:
•

Daily ozone hole area is the maximum daily ozone hole area on any day during ozone hole season.

•

15-day average ozone hole area is based on a 15-day moving average of the daily ozone hole area.

•

Ozone hole depth (or daily minima) is based on the minimum column ozone amount on any day
during ozone hole season.

•

The 15-day average ozone hole depth (or minima) is based on a 15-day moving average of the daily
ozone hole depth.

•

Minimum average ozone is the minimum daily average ozone amount (within the hole) on any day
during ozone hole season.

•


Daily maximum ozone deficit is the maximum ozone deficit on any day during ozone hole season.

•

Ozone deficit is the integrated (total) ozone deficit for the entire ozone hole season.

From Table 1 it can be seen that the 2014 ozone hole was one of the smallest holes since the late 1980s
with it ranking between the 16th and 21st out of 35 years of TOMS/OMI satellite records.

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 18


Table 1. Antarctic ozone hole metrics based on TOMS/OMI satellite data - ranked by size or minima (Note: 2005 metrics are average of TOMS and OMI data).
15-DAY AVERAGE
OZONE HOLE AREA
RAN
K

1
2
3
4
5
6
7
8
9
10
11

12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35

YEAR

2000
2006
2003

1998
2008
2001
2005
2011
1996
1993
1994
2007
2009
1992
1999
1997
2013
2014
2010
1987
2004
1991
1989
1990
2012
2002
1985
1986
1984
1988
1983
1982
1980

1981
1979

106 KM2

28.7
27.6
26.9
26.8
26.1
25.7
25.5
25.1
25.0
24.8
24.3
24.1
24.0
24.0
24.0
23.3
22.7
22.5
21.6
21.4
21.1
21.0
20.7
19.5
19.3

17.7
16.6
13.4
13.0
11.3
10.1
7.5
2.0
1.3
0.2

DAILY OZONE HOLE
AREA MAXIMA

15-DAY AVERAGE
OZONE HOLE MINIMA

OZONE HOLE
DAILY MINIMA

DAILY MINIMUM
AVERAGE OZONE

DAILY MAXIMUM
OZONE DEFICIT

INTEGRATED OZONE
DEFICIT

YEAR 106 KM2


YEAR

YEAR

YEAR

YEAR

YEAR

200
0
200
6
200
3
199
8
200
5
200
8
199
6
200
1
201
1
199

3
199
9
199
4
200
7
199
7
199
2
200
9
201
3
201
4
200
4
198
7
199
1
201
0
200
2
198
9
201

2
199
0
198
5
198
4
198
6
198
8
198
3
198
2
198
0
198
1
197
9

2000
2006
1998
2001
1999
2011
2003
2005

2009
1993
1996
1997
2008
1992
2007
1991
1987
2004
1990
1989
2014
2010
2013
1985
2012
2002
1986
1984
1983
1988
1982
1980
1981
1979
1994

29.8
29.6

28.4
27.9
27.0
26.9
26.8
26.4
25.9
25.8
25.7
25.2
25.2
25.1
24.9
24.5
24.0
23.9
22.7
22.4
22.3
22.3
21.8
21.6
21.2
21.0
18.6
14.4
14.2
13.5
12.1
10.6

3.2
2.9
1.2

DU

93.5
93.7
96.8
98.9
99.9
100.9
101.9
102.8
103.1
104.0
106.0
107.2
108.9
111.5
112.7
113.4
115.7
116.0
117.8
120.4
124.3
124.3
127.8
131.8

131.9
136.0
150.3
156.1
160.3
169.4
183.3
200.0
204.0
214.7
NaN

2006
1998
2000
2001
2003
2005
1991
2011
2009
1999
1997
2008
2004
1996
1993
1992
1989
2007

1987
1990
2014
2013
2010
1985
2012
2002
1986
1984
1983
1988
1982
1980
1979
1981
1994

DU

85
86
89
91
91
93
94
95
96
97

99
102
102
103
104
105
108
108
109
111
114
116
119
124
124
131
140
144
154
162
170
192
194
195
NaN

2000
2006
1998
2003

2005
2001
1999
2009
1996
2008
2011
1997
2007
1993
1992
2014
1991
1987
1990
2010
2013
1989
2004
2002
2012
1985
1986
1984
1983
1988
1982
1980
1979
1981

1994

DU

138.3
143.6
146.7
147.5
148.8
148.8
149.3
150.4
150.6
150.8
151.2
151.3
155.1
155.2
156.3
160.0
162.5
162.6
164.4
164.5
164.7
166.2
166.7
169.8
170.2
177.1

184.7
190.2
192.3
195
199.7
210
210.2
210.2
NaN

2006
2000
2003
1998
2008
2001
2005
2011
2009
1999
1997
1996
1992
2007
1993
2014
1991
2010
1987
2013

1990
1989
2002
2004
2012
1985
1986
1984
1983
1988
1982
1980
1981
1979
1994

MT

45.1
44.9
43.4
41.1
39.4
38.5
37.7
37.5
35.7
35.3
34.5
33.9

33.5
32.9
32.6
30.7
26.6
26.2
26.2
25.1
24.3
23.6
23.2
22.8
22.5
14.5
10.5
9.2
7
6
3.7
0.6
0.6
0.3
NaN

2006
1998
2001
1999
1996
2000

2011
2008
2005
2003
1993
2009
2007
1997
1992
1987
2010
2014
1990
2013
1991
2004
1989
2012
1985
2002
1986
1984
1988
1983
1982
1980
1981
1979
1994


MT

2560
2420
2298
2250
2176
2164
2124
1983
1895
1894
1833
1806
1772
1759
1529
1366
1353
1252
1181
1037
998
975
917
720
630
575
346
256

198
184
73
13
4
1
NaN

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 19


Figure 6 shows the 15-day moving average of the minimum daily column ozone levels recorded in the hole
since 1979 from TOMS and OMI data. This metric shows a consistent downward trend in ozone minima
from the late 1970s until the mid-to-late-1990s, with signs of ozone recovery by 2014. The 1996-2001 mean
was 100±5 DU, while the 2009-2014 mean was 119±13 DU. There is a strong suggestion that ozone is
recovering with the uncertainties no longer overlapping (at 1σ level). The 2014 ozone hole is the fifth
smallest since 1988.
The orange line in Figure 6 (and in Figures 7, 8, 9 and 10) is a simple linear regression of Antarctic Equivalent
Effective Stratospheric Chlorine (EESC-A; 5.5 year lag) against the 15-day smoothed column minima (and the
other metrics in Figures 7, 8, 9 and 10), plotted against time. EESC is calculated from Cape Grim data – both
in situ and from the Cape Grim Air Archive – and AGAGE global measurements of Ozone Depleting
Substances (ODSs: chlorofluorocarbons, hydrochlorofluorocarbons, halons, methyl bromide, carbon
tetrachloride, methyl chloroform and methyl chloride (Fraser et al., 2014)). The regressed EESC broadly
matches the decadal variations in the ozone minima indicating a slow recovery since early to mid-2000s. It
also gives a guide to the relative importance of the meteorological variability, especially in recent years.

Figure 6. Minimum ozone levels observed in the Antarctic ozone hole using a 15-day moving average of the
minimum daily column ozone levels during the entire ozone season for all available years of TOMS (green) and OMI
(purple) data. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the
text. The error bars represent the range of the daily ozone minima in the 15-day average window.


If we simply remove the significantly dynamically-influenced 2002 ozone data from Figure 6, the remaining
data (1996-2014) show signs of ozone growth (recovery) of 1.3±0.4 (1σ) DU/yr.
Figure 7 shows the average ozone amount in the ozone hole (averaged column ozone amount in the hole
weighted by area) from 1979 to 2014 from TOMS and OMI data. This metric shows a consistent downward
trend in average ozone from the late-1970s until the late-1990s, with some sign of ozone recovery by 2014.
The 1996-2001 mean was 148±5 DU while the 2009-2014 mean was 160±8 DU. This is suggestive of the
commencement of ozone recovery, but the uncertainty intervals still (just) overlap.
If we remove the significantly dynamically-influenced 2002 and 2004 ozone data from Figure 7, the
remaining data (1996-2014) show signs of ozone growth (recovery) of 0.9±0.3 (1σ) DU/yr. This is also
indicated by the regressed EESC-A line.

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 20


Figure 7. The average ozone amount in the ozone hole (averaged column ozone amount in the hole weighted by
area) for all available years of TOMS (green) and OMI (purple) data. The orange line is obtained from a linear
regression to Antarctic EESC (EESC-A) as described in the text.

Figure 8 shows the maximum ozone hole area (15-day average) recorded since 1979 from TOMS and OMI
data. Disregarding the unusual years (1988, 2002, 2004) when the polar vortex broke up early, this metric
suggests that the ozone hole has stopped growing around the year 2000 (date of maximum ozone hole
area), and may now be showing signs of a decline in area. The 1996-2001 mean was (25.6 ±2.0) x106 km2,
while the 2009-2014 mean was (22.5±2.0) x106 km2, again indicative of the commencement of possible
ozone recovery, but not statistically significant.
If we remove the significantly dynamically-influenced 2002 and 2004 ozone data from Figure 8, the
remaining data (1996-2014) are starting to show a decrease in ozone hole area of (0.2±0.1) x106 km2/yr.

Figure 8. Maximum ozone hole area (area within the 220 DU contour) using a 15-day moving average during the
ozone hole season, based on TOMS data (green) and OMI data (purple). The orange line is obtained from a linear

regression to Antarctic EESC (EESC-A) as described in the text. The error bars represent the range of the ozone hole
size in the 15-day average window.

Figure 9 shows the integrated ozone deficit (Mt) from 1979 to 2014. The ozone deficit rose steadily from the
late-1970s until the late-1990s/early 2000s, where it peaked at approximately 2300 Mt, and then started to
drop back down. This metric is very sensitive to meteorological variability; however, if we exclude the 2002
data (when the ozone hole split in two due to a significant dynamical disturbance) then there appears to be
evidence of ozone recovery. The 1996-2001 mean was 2180±230 Mt while the 2009-2014 mean was

The 2014 Antarctic Ozone Hole and Ozone Science Summary: Final Report | 21


1380±510 Mt, suggesting the commencement of ozone recovery (uncertainties no longer overlapping at
1σ).
If we remove the significantly dynamically-influenced 2002 ozone data from Figure 9, the remaining data
(1996-2014) show signs of a decline in ozone deficit of 56±18 (1σ) Mt/yr.

Figure 9. Estimated total ozone deficit for each year in millions of tonnes (Mt), based on TOMS (green) and OMI
(purple) satellite data. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in
the text.

The most quoted (though not necessarily the most reliable) metric in defining the severity of the ozone hole
is the average minimum ozone levels observed over Halley Station (British Antarctic Survey), Antarctica,
throughout October (Figure 10). This was the metric that was first reported in 1985 to identify the
significant ozone loss over Antarctica. Based on this metric alone, it would appear that October mean ozone
levels over Halley may have started to increase again. The minimum ozone level was observed in 1993,
which has been attributed to residual volcanic effects (Mt Pinatubo, 1991). Ignoring the warm years of 2002
and 2004, the mean October ozone levels at Halley Station for 2009 to 2014 (166±18 DU) are higher than
those observed from 1996 to 2001 (141±4 DU), and now appear statistically significant at the 1 σ
uncertainty level.

If we remove the significantly dynamically-influenced 2002 and 2004 ozone data from Figure 10, the
remaining data (1996-2014) show significant ozone growth (recovery) of 1.5±0.6 (1σ) DU/yr. For the period
1993-2014 the ozone growth is 1.8±0.4 (1σ) DU/yr, although the early 1990s data may be low due to the
impact of the Mt Pinatubo eruption.

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Figure 10. Total column ozone amounts (October mean) as measured at Halley Station, Antarctica, by the British
Antarctic Survey from 1956 to 2014. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A)
as described in the text.

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4 Antarctic ozone recovery
Ozone recovery over Antarctica is complex to model. Apart from the future levels of ozone depleting
chlorine and bromine in the stratosphere, temperature trends and variability in the stratosphere, the
impact of major volcanic events and the future chemical composition (for example H 2O, CH4 and N2O) of the
stratosphere are likely to be important factors in determining the rate of ozone recovery. Model results and
observations show that the solar cycle changes have maximum impact on tropical ozone and do not
significantly impact on stratospheric ozone levels over Antarctica.
Equivalent Chlorine (ECl: chlorine plus weighted bromine) levels, derived from CSIRO Cape Grim and other
AGAGE surface and CSIRO Antarctic firn observations of ODSs, are likely to decline steadily over the next few
decades at about 1% per year, leading to reduced ozone destruction. Figure 11 shows Equivalent Effective
Stratospheric Chlorine for mid- (EESC-ML) and Antarctic (EESC-A) latitudes, derived from ECl using fractional
release factors from Newman et al. (2007), lagged 3 years (EESC-ML) and 5.5 years (EESC-A) to approximate
the time taken to transport ECl to these regions of the stratosphere.
EESC-A peaked at 4.12 ppb in 2000 and EESC-ML at 1.92 ppb in 1998 respectively, falling to 3.73 and 1.63
ppb respectively by 2014, declines of 9.5% and 15.1% respectively. Table 2 shows the species contributing to

the declines in EESC-A (~0.40 ppb) and in EESC-ML (~0.30 ppb) since their peak values in 2000 and 1998
respectively. The decline since 2000/1998 to 2014 is dominated by methyl chloroform, followed by methyl
bromide, the CFCs and carbon tetrachloride. The halons and HCFCs have made an overall growth
contribution to EESC-A and EESC-ML since 2000/1998.
Table 2. ODS contributions to the decline in EESC at Antarctic and mid-latitudes (EESC-A, EESC-ML) observed in the
atmosphere in 2014 since their peak values in 2000 and 1998 respectively.
Species

EESC decline
Antarctic
ppb Cl

EESC decline
mid-latitudes
ppb Cl

methyl chloroform

0.28

0.20

methyl bromide

0.12

0.08

CFCs


0.08

0.05

carbon tetrachloride

0.06

0.04

halons

-0.08

-0.04

HCFCs

-0.06

-0.03

Total decline

0.40

0.30

The initial (1-2 decades) decline in EESC-ML and EESC-A have been and will be dominated by the shorterlived ODSs, such as methyl chloroform and methyl bromide, whereas the long-term decline will be
dominated by CFCs and carbon tetrachloride. Based on EESC-ML and EESC-A values from scenarios of ODS

decline (Harris and Wuebbles, 2014), ozone recovery at mid-latitudes will occur at about the mid- to late2040s and ozone recovery in the Antarctic stratosphere will occur about the mid-2070s. This is now a few
years later than reported in the previous ozone assessment due to the updated longer estimated lifetimes
for CFC-11 and CCl4. These lead to slower atmospheric decay and thus an increased contribution to EESC in
the future.
In response to the need to easily convey information to the general public about the levels of ozonedestroying chemicals in the atmosphere, and when might the ozone hole recover, NOAA has developed the
Ozone Depleting Gas Index (ODGI) (Hoffman and Montzka, 2009; and recent updates see
The index neatly describes the state of the atmosphere, in relation
to stratospheric halogen (chlorine plus bromine) levels, and is based on atmospheric measurements of
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ODSs. The index has two components, one relevant for ozone-depleting chemicals and the ozone hole over
Antarctica (the ODGI-A), and one relevant for mid-latitudes (the ODGI-ML). Figure 12 shows the CSIRO
version of the ODGI-ML and ODGI-A indices derived from global AGAGE data including data from Cape Grim.
Based on data up to 2014, the ODGI-A and ODGI-ML indices have declined by 18% and 38% respectively
since their peak values in 2000 and 1998 respectively, indicating that the atmosphere in 2014 is 18% and
38% along the way toward a halogen level that should allow an ozone-hole free Antarctic stratosphere and a
‘normal’ (pre-1980s) ozone layer at mid-latitudes. The CSIRO version of the ODGI uses ODS fractional
release factors from Newman et al. (2007).

Figure 11. Equivalent Effective Stratospheric Chlorine for mid-and Antarctic latitudes (EESC-ML, EESC-A) derived from
global measurements of all the major ODSs at Cape Grim (CSIRO) and other AGAGE stations and in Antarctic firn air
(CSIRO) from Law Dome. EESC-A is lagged 5.5 years and EESC-ML 3 years to approximate the transport times for
ODSs from the Earth’s surface (largely in the Northern Hemisphere) to the stratosphere at Southern Hemisphere
mid- and Antarctic latitudes. Arrows indicate dates when the mid-latitude and Antarctic stratospheres return to pre1980s levels of EESC, and approximately pre-ozone hole levels of stratospheric ozone.

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