psc

張超鈞:

PSCs：Polar Stratospheric Clouds 極地同溫層雲冰晶上的表面異相反應將增加臭氧(ozone)的消耗。極地的同溫層雖然乾燥，但是因為低溫很低會使水蒸汽凝結成為冰晶，形成極地同溫層雲(PSCs)。南極地區比北極溫度低，極地旋渦會比在北極來得穩定，較易形成PSCs。 而PSCs被區分為兩類型，亦即所謂的Type I與Type II。Type I分為Type Ia與Type Ib.Type Ia組成為HNO3．3H20(NAT), 溫度~190-195 KType Ib組成為HNO3/H2SO4/H2O, 溫度~190-195 KType II PSCs為極低溫直接由水結成之冰晶，組成為H2O ice, 溫度~188-190 KPSCs表面上的異相反應使得活性低的氯暫存物種變成活性的氯氣，Cl2經過光分解後形成破壞臭氧的氯原子，致使臭氧洞(ozone hole)產生，其反應機制如下: HCl(s)+ClONO2 ---> Cl2+HNO3(s)Cl2+hν ---> 2 Cl2【Cl+O3 ---> ClO+O2】ClO+NO2+M ---> ClONO2+MNet:HCl(s)+NO2+2O2 ---> ClO+HNO3(s)+2O2南極PSCs較易形成，較容易產生臭氧洞。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.Atmosphere, Climate & Environment Good Website：http://www.ace.mmu.ac.uk/http://www.ace.mmu.ac.uk/eae/Ozone_Depletion/Older/PSCs.htmlhttp://www.ace.mmu.ac.uk/eae/Ozone_Depletion/ozone_depletion.html
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