ozone hole - cause and effects

8/11/2019 Ozone Hole - Cause and Effects

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THE OZONE HOLECAUSES AND EFFECTS


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INTRODUCTIONIn this section, we will discuss about the Ozone Hole

and its causes


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WHAT IS THE OZONE HOLE?

The ozone hole is an annual thinning of the ozone layerover Antarctica, caused by stratospheric chlorine. Othermore moderate thinnings have also been called "ozoneholes", such as that over the North Pole during certainweather conditions.

The discovery of the annual depletion of ozone above theAntarctic was first announced in a paper by Joe Farman,Brian Gardiner and Jonathan Shanklin which appearedin Nature in May 1985. The most pronounced decrease inozone has been in the lower stratosphere.

In 2012, it has been reported that the ozone hole haddecreased to the smallest size since 2002.


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CAUSES OF OZONE HOLE

Scientific evidence indicates that stratospheric ozone is beingdestroyed by a group of manufactured chemicals, containingchlorine and/or bromine. These chemicals are called "ozone-

depleting substances" (ODS). ODS are very stable, nontoxic and environmentally safe in the

lower atmosphere, which is why they became so popular inthe first place. However, their very stability allows them tofloat up, intact, to the stratosphere. Once there, they are broken

apart by the intense ultraviolet light, releasing chlorine andbromine. Chlorine and bromine demolish ozone at analarming rate, by stripping an atom from the ozone molecule.A single molecule of chlorine can break apart thousands ofmolecules of ozone.


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The Main Ozone-Depleting

Substances (ODS)In this section, we will discuss the chief molecules that

harm the Ozone layer


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Halons

Used in some fireextinguishers, in caseswhere materials and

equipment would bedestroyed by water orother fire extinguisherchemicals. In B.C.,halons cause greaterdamage to the ozonelayer than do CFCs fromautomobile airconditioners.


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Methyl Chloroform

Used mainly inindustry for vapourdegreasing, someaerosols, cold cleaning,adhesives andchemical processing.


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Carbon Tetrachloride

Used insolvents and

some fireextinguishers.


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Hydrofluorocarbons(HCFCs)

HCFCs have become major,transitional substitutes for CFCs.

They are much less harmful tostratospheric ozone than CFCs are. ButHCFCs they still cause some ozone

destruction and are potent greenhousegases.


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Health and Environmental Effects of

Ozone Layer DepletionIn this section, we will discuss the effects of the Ozone

Hole.


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Effects on Human Health

Laboratory andepidemiological studiesdemonstrate that UVB causesnon-melanoma skin cancer and

plays a major role in malignantmelanoma development. Inaddition, UVB has been linkedto cataracts -- a clouding of theeyes lens. All sunlightcontains some UVB, even withnormal stratospheric ozonelevels. Ozone layer depletionincreases the amount of UVBand the risk of health effects.


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Effects on Plants

Physiological anddevelopmental processes ofplants are affected by UVB

radiation, even by theamount of UVB in present-day sunlight. Despitemechanisms to reduce orrepair these effects and alimited ability to adapt toincreased levels of UVB,plant growth can bedirectly affected by UVBradiation.


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Effects on MarineEcosystems

Solar UVB radiation has beenfound to cause damage to earlydevelopmental stages of fish,shrimp, crab, amphibians andother animals. The most severeeffects are decreased reproductivecapacity and impaired larvaldevelopment. Even at currentlevels, solar UVB radiation is a

limiting factor, and small increasesin UVB exposure could result insignificant reduction in the size ofthe population of animals that eatthese smaller creatures.


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Effects on BiogeochemicalCycles

Increases in solar UV radiationcould affect terrestrial and aquaticbiogeochemical cycles, thus alteringboth sources and sinks ofgreenhouse and chemically-important trace gases e.g., carbondioxide (CO2), carbon monoxide(CO), carbonyl sulfide (COS) andpossibly other gases, includingozone. These potential changeswould contribute to biosphere-atmosphere feedbacks thatattenuate or reinforce theatmospheric buildup of these gases.


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Thank You!!A presentation by Shivam Agarwal

ozone hole - cause and effects

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