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The Warsaw Voice » The Polish Science Voice » November 28, 2013
Geophysics
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Ozone Layer Continues to Shrink
November 28, 2013   
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Ozone is a colorless, odorless form of oxygen in the Earth’s atmosphere that plays an important role in protecting living organisms from the harmful effects of UV radiation from the sun.


The Polish Academy of Sciences’ Institute of Geophysics in Warsaw is marking 50 years of regular measurements of the ozone layer in the atmosphere over Poland.

The institute conducts observations at its Central Geophysical Observatory at Belsk near Grójec, 45 km south of Warsaw. The observatory is part of a global ozone monitoring system and has provided valuable data for numerous research papers. “The results of our observations of ozone have been used to assess the accuracy of ozone measurements made by satellites orbiting the Earth,” says Prof. Janusz Krzyścin, head of the Department of Atmospheric Physics at the Institute of Geophysics.

The molecules of oxygen we breathe have two oxygen atoms. The concentration of ozone (molecules with three atoms of oxygen) in the air is low. The maximum concentrations of ozone in the atmosphere, of the order of several ozone molecules per million air molecules, are present in the stratosphere, at a height of about 30 km. If we gathered all the ozone contained in a vertical column of air above our heads at ground level, the layer would be 2 to 5 mm thick, depending on the time of year, the institute says.

Ozone is toxic to humans. In small quantities, it causes cough and headache, and in larger amounts it leads to pulmonary edema and death. However, ozone is essential for life on Earth. It strongly absorbs ultraviolet radiation from the sun reaching the upper atmosphere, which has a protective effect on living organisms. Excessive UV radiation is harmful to the eyes and skin in humans. It also has a close, well documented link to the formation of skin cancers, according to Krzyścin.

Since the mid-1980s, terrestrial and satellite observations have been showing disturbingly low levels of ozone in the atmosphere over Antarctica. In some areas, ozone depletion reached 40 percent. In some layers of the atmosphere over Antarctica, at an altitude of 15-20 km, the ozone has been completely depleted.

This phenomenon, which has become known as the “ozone hole,” is caused by chlorofluorocarbon (CFC) gases commonly used in the second half of the 20th century in aerosols and refrigerators, according to the Institute of Geophysics. These compounds ended up in the atmosphere, migrated toward the equator and there they were elevated into the stratosphere, from where they spread toward the poles. During their movement in the upper layers of the atmosphere, CFCs disintegrated under the influence of strong UV radiation. The resulting free chlorine atoms then became a catalyst for chemical reactions leading to intensive decomposition of ozone. After about five years of wandering around in the stratosphere, CFCs reached Antarctica and the Arctic.

“As a result of the cooling of Antarctica during the polar night, in the period from June to September, in the southern hemisphere atmosphere, at an altitude of about 20 km, specific clouds appear composed of droplets of dilute nitric acid or ice crystals. With the return of sunlight over the area, in late August and early September, intensive ozone-depleting chemical reactions take place in the vicinity of such particle clouds. During the Arctic spring, the sun gradually warms up the atmosphere and clouds disappear, usually at the end of November, and the ozone hole also disappears with them,” says Krzyścin.

The ozone hole is a seasonal phenomenon. It has been appearing over the Antarctic each year at the end of winter and disappearing after a few months for over 30 years. Its size and duration depend on the weather conditions. The ozone hole over Antarctica has no effect on ozone levels over Poland. This country can only be threatened by the ozone hole over the Arctic. Over the north pole, however, the atmosphere is warmer, and only after the extremely cold winter of 2010/2011 did an ozone hole appear there. It was much less extensive than its counterpart over Antarctica.

Since the beginning of the 1970s, the stratosphere has been increasingly polluted with ozone-depleting substances. In the 1990s, measurements at the Institute of Geophysics observatory showed the ozone deficit over Poland at a level of 6 percent in relation to the long-term average from the 1960s and 1970s. These changes have resulted in a slight, almost harmless increase in UV radiation.

In 1987, under the so-called Montreal Protocol, the international community took action to reduce the emissions of CFCs and other ozone-depleting substances into the atmosphere. At the end of the 1990s, many observatories, including the one in Belsk, began to record a gradual increase in ozone concentrations in the atmosphere.

It seemed that with the Montreal Protocol and its subsequent revisions, imposing further restrictions on the production of substances harmful to the ozone layer, the problem had been resolved. However, in the middle of the last decade, the trend reversed and ozone levels began to drop again in our latitudes, the Institute of Geophysics says.

“It is possible that a new, as yet unidentified local mechanism that reduces the thickness of the protective ozone layer is beginning to operate in the atmosphere,” says Krzyścin.
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