A hole develops in the ozone layer

Beginning of an international measurement campaign in the Antarctic
On 14th June an international measurement campaign, lead by scientists
from the Alfred Wegener Institute's Potsdam research centre, will begin
in the Antarctic, with the aim of uncovering the still unclear processes
of ozone destruction during the Antarctic twilight. Nine measurement
stations in the Antarctic, including the German Neumayer Station run by
AWI, will release hundreds of weather balloons over the course of four
months, providing a precise picture of when, where and how fast the
ozone is destroyed.

Observation of air masses
The staff of the Neumayer Station have been selected especially for the
campaign: Ina Weber became the tenth overwinterer in December
2002, and her main task for the next few months will be the precisely
timed release of the ozone sondes. The sondes climb to a height of
around 35 kilometres, attached to a helium balloon, and measure ozone
concentration throughout the journey. The exact start times for the
sondes at Neumayer and at eight other, international, measurement
stations will be determined shortly before launch with the aim of
profiling an air mass which has already been measured a second time.
This will allow ozone destruction in a given air mass to be monitored
directly. Project leader Dr Peter von der Gathen says
"The fact that ozone is destroyed in the Antarctic is already clear.
What interests us now is the exact timing of this process, so that we
can compare measurements with model results."

Learning in the south applies to the north
This measurement technique was developed to follow the weaker, and
therefore harder to detect, ozone destruction in the Arctic, and is
being used for the first time in the Antarctic. The current campaign is
part of the EU funded research project QUOBI (Quantitative Understanding
of of Ozone losses by Bipolar Investigations), and is supported by
several non-European countries. It will offer the possibility of
comparing the speed of ozone loss in the Arctic with that in the
Antarctic directly. This should clarify poorly understood processes
which occur during the polar twilight. Measurements made in previous
years in the Arctic showed faster destruction of ozone when the sun is
low in the sky than is expected from our current understanding of the
processes involved. The total mass of ozone lost in spring could also
not be explained in some years.
The data from the Antarctic should help to find the mechanisms for this
additional ozone loss. In order to estimate the future development of
the ozone layer, all processes affecting it must be well understood.

In the second half of September at the latest, the researchers expect
destruction of the Antarctic ozone at a height of between 15 and 20
kilometres to be complete, as has been observed for many years. With
the beginning of the Antarctic summer in December, the yearly ozone
destruction comes to an end, and the hole closes as ozone-rich air from
the surrounding areas mixes with the ozone-depleted air. For around 20
years the hole has formed between August and September over the
Antarctic. Chlorine radicals, freed through the release of
chlorofluorocarbons (CFCs) and other halogen molecules by industry, are
mostly responsible for the decay. Although the release of these
substances has been heavily curbed under international agreements, it
will be many years before their concentration in the atmosphere falls to
insignificant levels.

Bremerhaven, 5.6.03