Ozone Depletion in the Stratosphere

Ozone in the atmosphere protects us from the harmful ultraviolet radiations,and also acts as a pollutant near the ground forming a dense cloud in industrialized areas. Most of the ozone is present in stratosphere, some substances cause its depletion. This depletion besides causing human health problems, also cause other effects on forests, wildlife and climate of the area.

      About 90% of the atmospheric ozone is found in the stratosphere extending from about 12 to 50 km above the Earth's surface. The concentration is greatest in the lower stratosphere (15 to 30 km), and this ozone layer is called "good ozone"due to its protective role for living organisms including humans by filtering out about 95% of the sun's harmful ultraviolet radiations. Only 10% of ozone found near the ground is harmful pollutant as a component of urban smog. Chlorofluorocarbons (CFCs) and biojenik emissions of methane and nitrous oxide cheaply cause stratospheric ozone depletion. In the stratosphere, the formation and destruction of ozone is a continuous phenomenon. The rate of formation is equal to the rate of destruction by natural processes.

Causes of ozone depletion

In 1974, the chemists Sherwood Rowland and Mario Molina at the University of California-Irvine indicated that CFCs were lowering the average concentration of ozone in the stratosphere. They shocked both, the scientific community and the US $ 28 billion per year CFC industry by calling for an immediate ban of CFCs in spray cans. In 1988, DuPoint (CFC industry) agreed to stop producing CFCs. In 1995, Rowland and Molina received the Nobel prize in chemistry for their work.

Thomas Midgley, Jr., General motors chemist, discovered the first chlorofluorocarbons (CFC) in 1930. CFC are known as freons by trade names. 

                  Ozone Hole

Ozone depletion is a catalytic process. Ozone loss was first detected during 1950s in the stratosphere over the Antarctica by scientists at the Halley Bay research station. Since then ozone loss in the Antarctica was confirmed during each spring (October). The British Antarctic survey team, let by Joe Farman in 1985 reported that ozone layer over Antarctica had shrunk each year since 1970s. This thinning of ozone (i.e. depletion in ozone concentration) layer was referred to ozone hole, which now regularly occurs over Antarctica during spring each year.this springtime ozone layer thickness above Antarctica has declined rapidly from 280-325 Dobson Units (DU), between 1956 and 1972 about 94 DU in 1995. In September 1998 the hole was biggest (25 million square kilometres) in area.

                    Ozone hole was also confirm above Arctic in 1990. But ozone loss over Arctic is lesser (5 to 10%) compared to that over Antarctica (60 to 70%) during spring.

Effects of ozone depletion

CFCs and other ozone depleting chemicals (OCDs) are the primary culprits of ozone depletion.Increased UV radiation reaching the Earth surface due to ozone depletion in the stratosphere is harmful to human health, crops, forests, animals and materials such as paints and plastics. Some of the expected effects of decrease level of ozone in the atmosphere are as follows :

• Human health - sunburn; eye cataract; skin cancer; immune system suppression.

• Food and forests - reduced yield from some crop plants; reduced seafood suppliers from reduced phytoplankton; decreased tree growth (forest productivity).

•Wildlife - increased eye cataract in some species; decrease population of aquatic species; reduce population of surface phytoplankton; disrupted aquatic food web from reduce phytoplankton.

• Air pollution and materials - Increased acid production; increased photochemical smog; degradation of outdoor paints and plastics.

•Global warming- possible climate changes due to accelerated warming (the warming caused by decreasing ocean uptake of carbon dioxide from atmosphere by phytoplankton and CFCs acting as greenhouse gases)

    The various strategies for protecting stratosphere ozone include chiefly the alternatives for refrigeration sector, foam sector, aerosols and solvents and fire fighting sector being developed with time.