VPE 511: Environment and Environmental Hygiene (2+1)

DEPLETION OF OZONE LAYERS

Depletion of ozone layers

• Ozone layer is in stratosphere it is anatural sun screen filtring ultra violet rays from sunlight protecting living organisms for the past 450 million years. The thinning of the stratospheric ozone layer is referred to as ozone hole.

Pollutants causing O₃ depletion

• Among the pollutants which cause O₃ depletion, the prominent ones are CFC’s CH₄ and N₂O. Of these three pollutants, CFC’s are the most damaging gas of ozone layer and are used as coolants in refrigerators and air conditioners. They enter from the troposphere to the stratosphere and remain there for 65-110 years, depleting O₃.
• Anthropogenic emissions of CFC’s are the main cause of worrying seasonal ozone losses in both the hemispheres of our earth. Long-lived chloride compounds of CFC’s are mainly responsible for ozone losses.
• Markus Rex, an atmosphere scientist at the Alfred Wegener Institute of Polar and Marine Research in Potsdam, Germany, saw new data for the break – down rate of a crucial molecule, dichlorine peroxide (Cl2O2). The rate of photolysis (light activated splitting) of this molecule was extremely low in the wavelengths available in the stratosphere – much lower than the currently accepted rate.
• The rapid photolysis of Cl2O2 is a key reaction in the chemical model of ozone destruction developed 20 years ago. At least 60% of ozone destruction at the poles points only to an unknown mechanism.