Record-thin ozone layer over Nordic region
Sunburn risk increased by light reflecting from snow banks
A large hydrogen balloon ascends at a rate of five metres a second from the Sodankylä meteorological research station, carrying equipment to measure ozone in the upper atmosphere. The balloon goes up to the stratosphere at an altitude of 35 kilometres, where it bursts and the equipment falls back to earth.
The key measurements take place at between 15 and 25 kilometres, where a thick layer of ozone should be present at this time of the year.
“We have not seen such an extensive thinning of the ozone layer in the 21 years of measuring ozone. The layer is record-thin”, says research professor Esko Kyrö.
The ozone layer protects life on earth by filtering potentially harmful ultraviolet radiation from the sun.
During the weekend, the UV index in the south of Finland was at level 3, when it is normally 1.5 at this time of the year.
Special researcher Rigel Kivi follows the flight of the probe on a computer in the control room. He says that the thinning of the ozone layer affects the whole Nordic region, all the way south to the latitude of Helsinki.
The thin layer has hovered over Finland for at least a week.
Forecasts are that it will soon move eastward. Balloon probes are therefore being sent up every day.
“Children especially should protect their eyes with sunglasses and put sunblock on their faces if they go out skiing or on the ice. Reflected sunlight from the snow can double the UV index”, says Tapani Koskela, senior researcher of the Finnish Meteorological Institute.
Thin layers of clouds do not block UV radiation completely. In addition, in the early spring the rays on the skin easily go unnoticed until it is too late, because of the cool temperature outside.
“In the summer, the UV index can be between 5 and 6, but at that time, we can feel the sunshine and have the presence of mind to protect ourselves against it”, Koskela adds.
The World Health Organisation recommends protection against the sun if the UV index exceeds level 3.
The thinning of the ozone layer is attributed to the exceptionally cold temperatures in the northern part of the stratosphere. At about -80 degrees Celsius and less, the chill enhances the ozone-destroying effect of chlorofluorocarbons, or freons.
In cold conditions and sunlight these CFC compounds break up and turn into chlorine radicals, which destroy ozone.
Although there has been a sharp decrease in the use of CFCs, they stay in the upper atmosphere for decades.
An estimated two thirds of the ozone layer in the polar regions has been destroyed at the altitude of 20 kilometres, says Markus Rex of the German Alfred Wegener Institute, and the head of the balloon probe operation of 30 arctic observation stations.
Usually, ozone levels above Finland in the spring are about 420 Dobson units, but now it is between 250 and 270, indicating that there is about 35 – 40 per cent less protective ozone than is normally the case in the spring.
The winter polar cyclones in the stratosphere dissipate as spring advances. That is when the ozone-depleted polar air mass mixes with the surrounding air. Strong ozone depletion can continue to some degree through the spring and summer.
The polar cyclone is not always this cold. Greenhouse gases can warm the lower atmosphere, but the upper atmosphere remains cold.
“The observations suggest that cold winters in the stratosphere are colder than before. In the longer term, however, the ozone layer will return, and climate change might even speed this up”, Kivi says.
Ozone layer (Wikipedia)