臭氧层空洞 英文

PSCs promote the conversion of inorganic Cl and Cl reservoir species to active Cl
Polar Stratospheric Clouds (PSCs)
• PSCs first form as nitric acid trihydrate (HNO3.3H2O) once temperature drops to 195K. • As the temperature gets colder, larger droplets of water-ice with nitric acid dissolved in them can form. • PSCs occur at heights of 15-20km.
• Depletion occurs in the Antarctic spring
Special Features of Polar Meteorology
• During the winter polar night, sunlight does not reach the south pole. • A strong circumpolar wind develops in the middle to lower stratosphere; These strong winds are known as the 'polar vortex'. • In the winter and early spring, the polar vortex is extremely stable, sealing off air in the vortex from that outside. • The exceptional stability of the vortex in Antarctic is the result of the almost symmetric distribution of ocean around Antarctica. • The air within the polar vortex can get very cold. • Once the air temperature gets to below about -80C (193K), Polar Stratospheric Clouds (or PSCs for short) are formed.
Why do PSCs occur at heights of 15-20 km?
• The long polar night produces temperature as low as 183 k (-90oC) at heights of 15 to 20 km. • The stratosphere contains a natural aerosol layer at altitudes of 12 to 30 km.
Polar vortex
• The polar vortex is a persistent large-scale cyclonic circulation pattern in the middle and upper troposphere and the stratosphere, centered generally in the polar regions of each hemisphere. • The polar vortex is not a surface pattern. It tends to be well expressed at upper levels of the atmosphere (> 5 km).
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October ozone hole over Antarctic
Features of the ozone hole
• Ozone depletion occurs at altitudes between 10 and 20 km
– If O3 depletion resulted from the ClOx cycle, the depletion would occur at middle and lower latitude and altitudes between 35 and 45 km. – The ClOx cycle requires O atom, but in the polar stratosphere, the low sun elevation results in essentially no photodissociation of O2. – The above observation could not be explained by the ClOx destruction mechanism alone.
The Ozone Hole
The discovery of the ozone hole
• The British Antarctic Survey has been monitoring, for many years, the total column ozone levels at its base at Halley Bay in the Antarctica. • Monitoring data indicate that column ozone levels have been decreasing since 1977. • This observation was later confirmed by satellite data (TOMS-Total Ozone Mapping Spectrometer) – Initially satellite data were assumed to be wrong with values lower than 190DU