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Ozone Layer

Depletion

Prepared by Piyush & Ilaxi © 2014 - Brilliant Classes by Piyush

Following topics are covered in a given module • What is Ozone? • What is Ozone?

• What is Ozone Layer?

• Causes of Ozone layer depletion

• Ozone depletion substances

• Role of CFCs ,HCFCs, Chlorine atoms and other pollutants

• Ozone hole

• Mechanism of hole formation

• Effects of Ozone depletion

• As a human being what can we do to protect Ozone layer?

© 2014 - Brilliant Classes by Piyush

What is ozone? • Ozone is a gas made up of molecule that

are formed by three oxygen atoms.

• Its molecule formula is O3.

• Ozone is formed when the sunlight hits oxygen molecules (O2) and breaks them up into individual atoms.

• These individual atoms then join up with O2 molecules and make O3 or ozone.


What is the ozone layer? • The ozone layer refers to the ozone in the

stratosphere; where more than 90% of the earth's ozone resides.

• The ozone layer absorbs much of the sun’s UV light. So, the ozone layer helps to protect us.

• The ozone layer, situated in the stratosphere about 15 to 30 km above the earth's surface.


Causes of Ozone Depletion • Depletion of the ozone layer is due to the emission of a

set of chemicals that cause ozone to convert into oxygen.

• Ozone blocks ultraviolet radiation’

• Ozone-Depleting Substances are:

• CFCs,

• HCFCs,

• halons,

• methyl bromide,

• carbon tetrachloride

• methyl chloroform. © 2014 - Brilliant Classes by Piyush

Depletion of Ozone Layer


• Most of the depletion of the ozone layer has been attributed to pollutants containing chloride (chlorofluorocarbons or CFCs). CFCs were used in refrigeration and air conditioning systems and as propellants in spray cans.

• These chemicals serve as a catalyst in a chemical reaction that converts ozone to oxygen. The presence of ice crystals accelerates the process.

• CFCs are not consumed in the reaction but remain in the stratosphere to continue the destruction of the ozone. © 2014 - Brilliant Classes by Piyush

• HCFCs are CFCs that contain hydrogen. This makes them more reactive to the OH radical, decreasing their tropospheric lifetime.

• “Hard” CFCs are unreactive to OH and other reactive radicals in the troposphere.

• They are also pretty insoluble in water.

• That means their tropospheric lifetimes are easily long enough that the majority of tropospheric CFCs pass through the tropopause into the stratosphere.


• Many CFCs absorb in the “UV window” (centered at 205 nm) between strong O2 and O3 absorption. That means most can photo dissociate in the bottom half of the stratosphere.

• Photodissociation releases chlorine atoms:

• For example: CFCl3 + light CFCl2 + Cl (l < 225 nm)


• Chlorine atoms deplete odd oxygen (Ox) largely by the following cycle

• Cl + O3 ClO + O2 • ClO + O Cl + O2

• Chlorine undergoes a series of reactions to form a

variety of compounds.

• Some of these are active in depleting ozone: Cl, ClO

• Some of these do not directly deplete ozone; these are chlorine reservoirs: HCl, ClONO2, HOCl


• The most important (long-lived) stratospheric chlorine reservoir is HCl .

• The reservoirs can become activated by various processes such as Photodissociation or reaction with OH.

• Loss of stratospheric chlorine occurs when they cross-back into the troposphere and are removed from the atmosphere.

• Most common route: HCl crosses back, dissolves in water, and is washed out.


Ozone Hole

• The ozone hole is defined as the area having less than 220 Dobson units (DU) of ozone in the overhead column (i.e., between the ground and space).

• The “ozone hole” is a sudden, marked depletion of ozone – a loss of 50% or more of total column ozone – in the lower stratosphere of the Antarctic in the weeks after the Spring sunrise.

• In 1985 the area of the hole was 10 million sq. km (and growing yearly).


Hole Formation Based on Two different mechanisms:

• Meteorological mechanism

• Movement of air from one place to another in the upper stratosphere.

• Cold temperature in the upper atmosphere causes nitric acid to freeze into crystals forming wispy pink clouds.

• Forms a vortex of tightly twisted winds thus forming a hole in the upper atmosphere.


Chemical Mechanism • Different chemicals are responsible for the

destruction of the ozone layer.

• chlorofluorocarbons (CFC’s) is man-made, non-toxic and inert in the troposphere.

• In the stratosphere they are photolysed, releasing reactive chlorine atoms that catalytically destroy ozone.

• A combination of low temperatures and elevated chlorine and bromine concentrations are responsible for the destruction of ozone in the upper stratosphere thus forming a “hole”.


Effects of Ozone depletion

• Skin Cancer (melanoma and nonmelanoma)

• Premature aging of the skin and other skin problems

• cataracts and other eye damage

• Immune system suppression


What can we do? • If you have a refrigerator made before 1995 it

probably uses refrigerant made from CFCs. Get a new refrigerator and be sure to have the old one disposed of properly.

• Old air conditioners, made before 1994, typically used a CFC called Freon.

• Even newer air conditioners use chemicals called HCFCs. Even though HCFCs are better for the ozone, they still contributes to the depletion, so try and use as little air conditioning as possible.


• A lot of foam products contain CFCs. Try and use different packing materials such as crumpled old newspapers.

• Protect yourself against sunburn. Minimize sun exposure during midday hours (10 am to 4 pm). Wear sunglasses, a hat with a wide brim, and protective clothing with a tight weave.

• Use a broad spectrum sunscreen with a sun protection factor (SPF) of at least 15 and 30 is better. © 2014 - Brilliant Classes by Piyush

ozone layer deplition - home - worth county schools...ozone hole •the ozone hole is defined as the...

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