CBSE Class 11-science Answered

Ozone hole:

• It is a loss of stratospheric ozone in springtime over Antarctica, peaking in September.
• It is defined as the size of the region with total ozone below 220 Dobson units (DU).
• Dobson Units are a unit of measurement that refer to the thickness of the ozone layer in a vertical column from the surface to the top of the atmosphere.
• Prior to 1979, total column ozone values over Antarctica never fell below 220 DU.
• The hole is a result of human activities--the release of huge quantities of chlorofluorocarbons (CFCs) and other ozone depleting substances into the atmosphere.

Consequences of ozone depletion in the stratosphere:

• For every 1% decrease in the stratospheric ozone the biologically active uv radiation will increase by 1.3%. The adverse effects of uv radiations are:
• Cataract can be developed resulting in blurred vision and without treatment, blindness.
• Exposure can  lead to accelerate ageing, wrinkling and various forms of cancer.
• Interference with photosynthesis could result in lower yields.
• Radiation affects the growth of phytoplankton, the mainstay of ocean food chain.