Flights over Arctic provide data for investigating ozone hole depletion

The team of atmosphere researchers -- among them Stephan Borrmann, Professor at the Institute of Atmospheric Physics of Johannes Gutenberg University Mainz and one of the directors of the Max Planck Institute of Chemistry in Mainz -- hopes to discover how long the processes that result in the formation of the hibernal holes in the ozone layer at the polar caps actually take. It is also expected that the data collected during the flights undertaken with the high-altitude aircraft "M55 Geophysica" will provide insight into what effect climate change is having on the physical and chemical processes that influence the ozone layer. This would make it possible to extrapolate the future development of the ozone layer under the conditions obtained during on-going changes.

The chlorofluorocarbons (CFCs) released by humans on the surface of the earth are gradually transported into the stratosphere. Here the CFCs are exposed to powerful ultraviolet radiation which decomposes the chlorofluorocarbons to finally release chlorine. This chlorine usually reacts with other chemicals and is bound in substances such as hydrogen chloride vapor and chlorine nitrate, which are not detrimental to ozone. However, in the stratospheric clouds located over the poles, the clorine from CFCs can form aggressive ozone-destroying chlorine monoxide radicals (CIO).

Analysis of these clouds is thus essential to the research being conducted by the Mainz team under Stephan Borrmann. And it is these extraordinary but natural clouds that are formed only in the stratosphere over the Arctic and Antarctic regions during the cold of the polar winters that are implicated in the formation of the holes in the ozone layer.

"As the warming of the atmosphere attributable to climate change also has a direct effect on the physical and chemical processes associated with the ozone layer, we urgently need to conduct new research into this aspect," explains Professor Borrmann.

The scientists are able to directly analyze the properties of the particles making up these polar stratospheric clouds -- frozen droplets of ice and nitric acid with an approximate diameter of 3-20 micrometers -- using instruments attached to the aircraft. In order to be able to determine the rate and extent of ozone depletion, the scientists need to find out exactly what size these droplets are and how many of them are present in these polar stratospheric clouds (PSCs). The Mainz team is using additional instruments to evaluate the characteristics of ultrafine airborne aerosol particles that are also present in the stratosphere and play a role in the relevant processes.

Remarkably, the presence of meteoric dust was even detected in the stratosphere during the data-gathering flights conducted between mid-January and mid-March 2010. It has also proved possible to collect significant amounts of data directly from PSCs. "We were amazed to discover that there were surprisingly large particles present in polar stratospheric clouds. These has a diameter of up to 30 micrometers, and they were rapidly precipitated thanks to their weight. This causes the substances contained in them to be irreversibly removed from the stratosphere, thus promoting the process of ozone depletion," Borrmann explains.

Originally a Russian spy plane, M55 Geophysica is one of only three aircraft worldwide that are able to reach the stratosphere -- and it can do this while carrying a payload of nearly one ton of metering instruments and other equipment. Such flights are the only way in which the atmospheric researchers can collect the information they still need to understand the correlations between ozone depletion and climate change.

Researchers from nine countries are taking part in the measuring flights, which start from Kiruna, located in the Arctic Circle in northern Sweden. The campaign is part of the EU project "RECONCILE" (reconciliation of essential parameters for an enhanced predictability of arctic stratospheric ozone loss and its climate interactions) that is being coordinated by scientists of the Jülich Research Center.