Ozónová díra – anglicky

Ozon layer

Ozone

Ozone boils at the temperature of -11.9 °C. Under normal conditions it’s dark blue liquid. It has tendency to separate into O₂+O. The middle time of separation is three days at the temperature of 20 °C or three months at the temperature of -50 °C.

The amount of ozone is expressed in Dobson units, named after professor G. Dobson from the Oxford University. 1Dobson unit means that the total amount of ozone in vertical column would make layer thick 10-3 cm (0.001 cm). 300 D.U. would make 3mm thick layer. 80-90% of ozone can be found in the stratosphere (10-25 km) and 10-20% in the troposphere (up to 10 km). Ozone is poisonous, especially when you breath it. For example, ozone printers produce ozone.

Freons

Freon is derived from words fre (ezed) on. Other name for freons is Chlorofuorcarbons (CFC) and freons containing hydrogen are labeled HCFC. In the industry, CFC are labeled R+2-4 numbers.

The life expectancy of CFC-11 is 65 years and the life expectancy for CFC-12 is 130 years.

Destroying of ozone

Rowland and Mobia

Cl + O₃ = ClO + O₂

ClO + O = Cl + O₃

Later theory:

Cl + O₃ = ClO + O₂

ClO + ClO + M = Cl₂O2 + M

Cl2O₂ + hv = Cl + ClO₂

ClO₂ + M = Cl + O₂ + M

Chlorine needs stratosphere clouds for destroying ozone. They can be found above poles. That’s why the concentration of Cl* so high above poles.

The lowest ozone layer was measured in years 1993 and 1994 above South pole. Ozone layer had just 90 d.u., that’s only 40% of normal state. When ozone layer drops under 50% of its typical state, it’s supposed to be an ozone layer.

In years 1926 – 1969 there was slight increase of ozone layer by 0.19% every 10 years. But during the years 70-90 ozone dramatically decreased by 2.5% every ten years. Moreover, there was much higher decrease in 1990’s.

Future evaluation

In 1970’s emissions of freons raised by 10% every year. It would have caused 30% reduction of ozone layer by the year 2000. Now the forecast is better, because there was a reduction in use of CFC-11 and CFC-12 and the emissions in 1995 dropped to the level of year 1976.

There are two prognoses for the future:

• If the emissions of CFC will be constant on the level of year 19976, there is going to be reduction of ozone by 2% until year 2000, by 3-4% until year 2080 and about 4% until In the further future, the decrease would be about 6%.
• The second prognoses suppose better knowledge of Chemistry over the time and reduction of using freons. The minimum level of ozone would be reached in year 2000, then there wouldn’t be big changes for 10 to 20 years and the ozone layer should reach it’s original level in the second half of the 21^st century or at the end of the 21^st

In the year 2015, it’s supposed to be in use about 500 stratosphere airplanes, each for 300 passengers. The damage of ozone layer should vary from 0.25% up to 7%, which is much lower than by freons

International contracts

• On the conference of United Nations Environment Programme was signed Vienna’s contract about protection of ozone layer on March 22^nd 135 countries signed this contract.
• Montreal protocol about compounds distracting ozone layer was accepted on September16 1987. It’s protocol for Vienna’s contract. 148 countries signed it.
• London’s clause – June 26^th – 29^th The list of CFC compounds was expanded from 5 to 15 and the year, by which they should be completely prohibited, was set to 2000. 180 countries signed.
• Other clause of Montreal protocol was accepted in 1991 in Nairobi
• Kodan’s clause – CFC shouldn’t be made after January 1^st 1996 and halons shouldn’t be made after January 1^st 37 countries signed this clause.

Bibliography

Ing. Erich Lippert, Ozonová vrstva Země, Vesmír 1995

Vaníček, K.: Globální změny ozónové vrstvy a jejich projevy nad územím Československa. ČHMÚ, Praha, 1992.

Novotný, V., Kotaška, M., Řeháček, V.: Londýnská konference a revize Montrealského protokolu o látkách narušujících ozónovou vrstvu Země, 1991