What are polar stratospheric clouds?

Question

What are polar stratospheric clouds?

Answer 1

The lower stratosphere over the south pole is the coldest spot on Earth.From June to September,cold winds blow around the region which prevent warmer air from entering.

Small amount of water vapour in the stratosphere freezes and forms thin clouds of ice crystals as the temperature in the lower stratosphere drops below -80 (minus 80) degree celcius.They are called polar stratospheric clouds.

These ice crystals convert safe molecules like CONO2 and HCL to more reactive ones like HOCL and CL2.Theses two compounds release CL atoms.At polar stratospheric temperatures,this sequence is extremely fast and it dominates the ozone-destruction process.

The Arctic polar vortex is much weaker than the Antarctic,as Arctic temperatures are several degrees higher and polar stratospheric clouds are less common, and tend to break up earlier in the spring.That is why ozone hole is confined to Antarctic only.

Answer 2

Polar stratospheric clouds (PSCs) are the medium on which reservoir chlorine compounds are converted into ozone-destroying chlorine radicals. (1)

They participate in a chain of events that results in the depletion of stratospheric ozone by man-made chlorine. (2)

Polar stratospheric clouds (PSCs) are important components of the ozone depletion process in the polar regions of Antarctica and the Arctic. PSCs provide the surfaces upon which chemical reactions involved in ozone destruction take place. These reactions lead to the production of free chlorine and bromine, released from CFCs and other ozone depleting chemicals (ODCs), which directly destroy ozone molecules.

Polar stratospheric clouds (PSCs), also known as mother-of-pearl or nacreous clouds, have been observed for many years. As their name suggests, the clouds form in cold polar stratospheric winters where, despite the dryness of the stratosphere, the temperature drops low enough for condensation to occur. PSCs are believed to be made of nitric acid and ice. In other parts of the world the stratosphere is too warm for these clouds to form, which is one reason why the "ozone hole" is confined to the Antarctic region. (3)