Ozone depletion

                                       Ozone depletion

              Ozone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions.

              The latter phenomenon is referred to as the ozone hole. There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric events.

External audio
“Whatever Happened to the Ozone Hole?”, DistillationsPodcast Episode 230, April 17, 2018, Science History Institute

The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbonrefrigerants, solvents, propellants, and foam- blowing agents(chlorofluorocarbons (CFCs), HCFCs, halons), referred to as ozone-depleting substances (ODS).

                 The Montreal Protocol is considered the most successful international environmental agreement to date.

 External links ::- 

• Ozone layer depletion
• Stratospheric ozone depletion
  
• Protection of the ozone layer
  

                       Ozone depletion and the ozone hole have generated worldwide concern over increased cancer risks and other negative effects. 

 

                                        The ozone layer prevents most harmful wavelengths of ultraviolet (UV) light from passing through the Earth's atmosphere. These wavelengths cause skin cancer, sunburn, permanent blindness, and cataracts, which were projected to increase dramatically as a result of thinning ozone, as well as harming plants and animals. 

                    These concerns led to the adoption of the Montreal Protocol in 1987, which bans the production of CFCs, halons, and other ozone-depleting chemicals.

      

                                  

                                 Theban came into effect in 1989. Ozone levels stabilized by the mid-1990s and began to recover in the 2000s, as the shifting of the jet stream in the southern hemisphere towards the south pole has stopped and might even be reversing.

                                       

                                    ^Recovery is projected to continue over the next century, and the ozone hole is expected to reach pre-1980 levels by around 2075.^In 2019, NASA reported that the ozone hole was the smallest ever since it was first discovered in 1982.

 Facts , effects and solutions of ozone depletion ::-

      

                                Ozone depletion, gradual thinning of Earth’s ozone layer in the upper atmosphere caused by the release of chemical compounds containing gaseous chlorine or bromine from industry and other human activities. The thinning is most pronounced in the polar regions, especially over Antarctica. 

                        Ozone depletion is a major environmental problem because it increases the amount of ultraviolet (UV) radiation that reaches Earth’s surface, which increases the rate of skin cancer, eye cataracts, and genetic and immune systemdamage. The Montreal Protocol, ratified in 1987, was the first of several comprehensiveinternational agreements enacted to halt the production and use of ozone-depleting chemicals. As a result of continued international cooperation on this issue, the ozone layer is expected to recover over time.

ozone depletionAntarctic ozone hole, September 17, 2001.NASA/Goddard Space Flight Center
1..Ozone hole and it's causes ::-

Ozone hole in North America during 1984 (abnormally warm, reducing ozone depletion) and 1997 (abnormally cold, resulting in increased seasonal depletion). Source: NASA^[35]

                                  The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 33 percent of their pre-1975 values. The ozone hole occurs during the Antarctic spring, from September to early December, as strong westerly winds start to circulate around the continent and create an atmospheric container. Within this polar vortex, over 50 percent of the lower stratospheric ozone is destroyed during the Antarctic spring.

                    As explained above, the primary cause of ozone depletion is the presence of chlorine-containing source gases (primarily CFCs and related halocarbons). In the presence of UV light, these gases dissociate, releasing chlorine atoms, which then go on to catalyze ozone destruction. 

                   The Cl-catalyzed ozone depletion can take place in the gas phase, but it is dramatically enhanced in the presence of polar stratospheric clouds(PSCs).

2.. world ozone day ::-

                              In 1994, the United Nations General Assembly voted to designate September 16 as the International Day for the Preservation of the Ozone Layer, or "World Ozone Day",to commemorate the signing of the Montreal Protocol^on that date in 1987.
3.. consequences of ozone layer depletion ::-
                       Since the ozone layer absorbs UVB ultraviolet light from the sun, ozone layer depletion increases surface UVB levels (all else equal), which could lead to damage, including an increase in skin cancer. This was the reason for the Montreal Protocol.                              Although decreases in stratospheric ozone are well-tied to CFCs and increases in surface UVB, there is no direct observational evidence linking ozone depletion to higher incidence of skin cancer and eye damage in human beings. This is partly because UVA, which has also been implicated in some forms of skin cancer, is not absorbed by ozone, and because it is nearly impossible to control statistics for lifestyle changes over time. Ozone depletion may also influence wind patterns.
Types ::-

• Increased uv
• Biological effects
• Basal and squamous cell carcinomas
• Malignant melanoma
• Cortical cataracts
• Increased tropospheric
• Increased production of vitamin d
• Effects on animal
• Effects on crop
• Effects on plant life

                      The ban came into effect in 1989. Ozone levels stabilized by the mid-1990s and began to recover in the 2000s, as the shifting of the jet stream in the southern hemisphere towards the south pole has stopped and might even be reversing.

                          ^Recovery is projected to continue over the next century, and the ozone hole is expected to reach pre-1980 levels by around 2075 In 2019, NASA reported that the ozone hole was the smallest ever since it was first discovered in 1982.