Merged total ozone from GOME, SCIAMACHY and GOME-2 from June
1995 until May 2009.
Credits: Diego Loyola, DLR

21 September
2009 European Space Agency

By merging more than a decade of atmospheric data from European
satellites, scientists have compiled a homogeneous long-term ozone record
that allows them to monitor total ozone trends on a global scale – and the
findings look promising.
 
Scientists merged monthly total ozone data derived from the vertically
downward-looking measurements of the GOME instrument on ESA’s ERS-2
satellite, SCIAMACHY on ESA’s Envisat and GOME-2 on the European
Meteorological Satellite Organization’s MetOp-A.

“We found a global slightly
positive trend of ozone increase of almost 1% per decade in the total ozone from
the last 14 years: a result that was confirmed by comparisons with ground-based
measurements,” said Diego G. Loyola R. who worked on the project with colleagues
from the German Aerospace Center (DLR).

Ozone is a protective layer found
about 25 km above us mostly in the stratospheric layer of the atmosphere that
acts as a sunlight filter shielding life on Earth from harmful ultraviolet rays.
The thinning of this layer increases the risk of skin cancer, cataracts and harm
to marine life.  



Monthly mean total ozone averaged over 60°N to 60°S from the
merged GOME, SCIAMACHY and GOME-2 datasets (solid lines). The original datasets
(dashed lines) before the adjustment are plotted for comparison.

Credits: Diego Loyola, DLR

The ozone layer is not
distributed evenly, with more changes occurring in the upper stratosphere. By
collecting data while looking sideways (limb viewing) rather than vertically
downwards, instruments are able to provide highly accurate measurements of the
stratosphere.

A team of scientists around
Ashley Jones and Jo Urban from Sweden’s Chalmers University of Technology
combined the limb measurements of US instruments SBUV, SAGE I+II and HALOE with
data from OSIRIS, SMR and SCIAMACHY on the European satellites Odin and Envisat
to analyse the long-term evolution of stratospheric ozone from 1979 to the
present. These data show a decrease in ozone from 1979 until 1997, and a small
increase since then.

“Our analysis shows that upper
stratospheric ozone declines at northern and southern mid-latitudes at roughly
7% per decade during 1979–97, consistent with earlier studies based on data from
satellites and ground networks. A clear statistically significant change of
trend can be seen around 1997. The small increase (of 0.8–1.4% per decade)
observed thereafter, from 1997 to 2008, is however not yet statistically
different from a zero trend. We hope to see a significant recovery of (upper
stratospheric) ozone in the next years using longer, extended satellite
time-series,” Urban said.

Upper stratospheric (35-45km) ozone anomalies for six instruments at
northern mid-latitudes (30N–60N). Shown are SAGE I+II (blue, A), SBUV/2
(orange, B), UARS/HALOE (red, C), Odin/SMR (magenta, D), Odin/OSIRIS
(black, E), and Envisat/SCIAMACHY (cian, F). Also shown under-laid is the
all instrument average (green). Thin black lines indicate the fitted
trends before and after 1997.

Citation: Based on slide by Jo Urban, adapted from A. Jones, J. Urban, D.P.
Murtagh, P. Eriksson, S. Brohede, C. Haley, D. Degenstein, A. Bourassa, C. von
Savigny, T. Sonkaew, A. Rozanov, H. Bovensmann, and J. Burrows, Evolution of
stratospheric ozone and water vapour time series studied with satellite
measurements, Atmos. Chem. Phys., 9, 6055–6075, 2009

The thinning of the ozone layer
is caused by chemicals such as human-produced bromine and chlorine gases that
have long lifetimes in the atmosphere. The Montreal Protocol (1987) was
introduced to regulate and phase out the production of these substances. Its
effect can clearly be seen in the satellite observations of ozone and these
chemicals. Using SCIAMACHY data in limb-viewing observation mode from 2002 to
2008, François Hendrick from the Belgian Institute for Space Aeronomy
(BIRA/IASB) and his colleagues from the University of Bremen performed a trend
analysis of bromine monoxide (BrO) in the stratosphere. BrO is a highly
efficient catalyst in ozone destruction. The results show a negative trend in
BrO abundance in the stratosphere during this period, marking the first time a
decline in stratospheric bromine has been reported from a spaceborne
observation.

Time series of monthly averaged BrO column abundances measured
over Harestua (60°N, 11°E) by SCIAMACHY limb (right) and ground-based UV-visible
(left) instruments. Thick lines indicate trend analysis results. A decline of
-0.6+/-0.3% per year is estimated from SCIAMACHY limb observations over the
2002-2008 period, which is in good agreement with ground-based UV-visible
measurements (-0.7+/-0.3%/year).

Credits: F. Hendrick (BIRA/IASB) and A. Rozanov (IUP/IFE-Bremen), 2009

Using SCIAMACHY data in
limb-viewing observation mode from 2002 to 2008, François Hendrick from the
Belgian Institute for Space Aeronomy (BIRA/IASB) and his colleagues from the
University of Bremen performed a trend analysis of bromine monoxide (BrO) in the
stratosphere. BrO is a highly efficient catalyst in ozone destruction. The
results show a negative trend in BrO abundance in the stratosphere during this
period, marking the first time a decline in stratospheric bromine has been
reported from a spaceborne observation.

“The good agreement with
ground-based observations at high and mid-latitudes show that SCIAMACHY limb
data can be used for stratospheric BrO trend monitoring. These findings provide
strong evidences that the Montreal Protocol restrictions on brominated
substances have now reached the stratosphere,” Hendrick said. Having access to
these atmospheric satellite data over long periods is important for scientists
to identify and analyse long-term trends and changes. In addition to monitoring
ozone trends, scientists will continue to monitor ozone-depleting substances
that were phased out under the Montreal Protocol but continue to linger in the
atmosphere. All of these results were presented at ESA’s five-day ‘Atmospheric
Science Conference’ held in Barcelona, Spain, 7–11 September. The objective of
the conference was to provide scientists and researchers with the opportunity to
present up-to-date results from their atmospheric research and application
projects using space-based atmospheric sensors. The conference, with some 200
participants, included presentations that detail the current use of satellite
instruments for remote sensing of trace gases in the stratosphere and
troposphere, clouds and aerosols, pollution and greenhouse gas monitoring.


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