Ozone layer depletion and Ozone layer depletion and Global warming Global warming

Part 1

Ozone layerOzone and Ozone layer:

• Ozone gas is found on the lower portion of the stratosphere at the height of about 20km above the earth in the form of a layer called ozonosphere.

• Stratospheric ozone is typically measured in Dobson Units (DU), which is the number of molecules required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0 degrees Celsius and an air pressure of 1 atmosphere (the pressure at the surface of the Earth). 

Ozone hole• The ozone layer was discovered in 1913 by the

French physicists Charles Fabry and Henri Buisson.

• Ozone hole was detected at first in 1975.

• Some British scientists noticed effects of O3 hole in 1985.

• Ozone hole can caused by some green house gases (GHGs).

Ozone hole• In 1979—when scientists were just coming to

understand that atmospheric ozone could be depleted—the area of ozone depletion over Antarctica grew to 1.1 million square kilometers, with a minimum ozone concentration of 194 Dobson Units.

• In 1987, as the Montreal Protocol was being signed, the area of the hole reached 22.4 million square kilometers and ozone concentrations dropped to 109 DU.

Ozone hole• By 2006, the worst year for ozone depletion to

date, the numbers were 29.6 million square kilometers and just 84 DU.

• By 2011, the most recent year with a complete data set, the hole stretched 26 million square kilometers and dropped to 95 DU.

Characteristics of Ozone layer

Function:• It regulates the weather and climate of the

earth.• It filters away the ultraviolet radiation and

protects the earth as protective layer.

Photochemical reaction:Ozone is an unstable gas and for its

formation destruction (photochemical reaction) process; UV ray is essential which come from the sun.

Characteristics of Ozone layer

Photochemical reaction:

O + O2 O3

O3 O + O2

In these processes a part of the harmful UV rays is converted in to infra-red (IF- infrared - wavelength is longer thas visible light) rays, which is not lethal to man however has heating effect.

UV

Cause of O3 depletion:

When ozone destruction is being greater then the formation known as ozone depletion.

CFCs, CCl4, CH4 etc. are main chemicals called halocarbons that used to check the ozone formation. These carbon compounds produce the chlorine, which breaks the O3 molecules and reduces O3 content in the atmosphere.

Reaction: Cl +O3 ClO + O2

ClO Cl + O

By this way; one atom of Cl is sufficient to destroy a lakh of ozone molecules.

Cause of O3 depletion:

• Destruction of ozone molecules lead the destruction of ozone layer. Therefore, harmful UV (ultra violate radiation) got chance to come through the ozone layer and fall on the earth surface.

• UV is lethal to all living being.

Form of UV coming from sun:

We know that the visible light range is about differ than the UV or IF rays.

Earth receives UV radiation in 3 forms:– UVA in the wavelength range 315-400 NM– UVB in the wavelength range 289-314 NM– UVC in the wavelength range 100-280 NM

Among these UV-B is most dangerous.

Effects of UV rays

Presence of UV (estimated)The effects of O3 depletion eventually increase the UV

rays penetration to the surface of the earth.

• 1% drops in stratospheric O3 increase 2-3 % UV.

• In this century (21st) UV rays may be increase 3-4% at the tropics and 10-12 % at high altitude.

Effects on Agricultural crops:• Agricultural crop losses.• Increase food production costs because of physical

damages of growing plant.

• Damage is also spread in other plants of the

earth’s physical ecosystem.

Effects of UV rays:Effects of UV rays:

Effects on health:• Sunburn, Ageing, Wrinkling of skin.• Destruction of protein, Mutation of genes.• EPA ( Environmental Protection Agency)

said-– By increasing of 1% UVB rays increases basal

cell cancer1% and squamous cell cancer 2%.– It may caused melanoma skin cancer– Cataracts disease in eye by about 0.2%.

Ozone hole improvementOzone hole improvement• The average size of the 2012 ozone hole

was 6.9 million square miles (17.9 million square kilometers).

• Argentine scientists agree that there are signs of recovery of the ozone layer that protects life on earth by filtering out the sun’s harmful ultraviolet radiation.

Importance of CFCs at the beginning

• CFCs-11 and CFCs-12 developed in 1930s as a refrigerants (refrigeration, building and mobile air conditioning). Because it is:

– Extremely stable, – Nontoxic – Inert– Relative to the electrical and mechanical

machinery.

• By 1970s, it had been used as- Aerosol propellant in the hair spray, deodorants, insecticide etc.

Importance of CFCs at the beginning

• Later on it was started to use in various industries as an industrial blowing agent for manufacturing:

– flexible, rigid plastic foams.– polyurethane and polystyrene foams and– industrial cleaning agents and solvents

• CFC-113 was started to use as a solvent, especially for microelectronic production.

CFCs are one of the important causes for ozone layer depletion.

People start thinking about the alternatives to way out of this

risk!!

Alternative sources of CFCs

Two viable substances in the form of HCFC and HFC-34 are considered to be harmless for ozone.

Out of these two HFC-34 is the less harmful because, absence of chlorine in it but it has some problem:

– It is expensive.– Inflammable.– Toxic in nature.

So, we can use instead of these Butane, Propane because it is—

– Less expensive.– Less harmful.– Freely available.

Today’s Propellants:

• Hydro-fluoro carbons (HFCs)• Hydrofluoralkanes (HFA)

- Used in inhaler.

• Chloro-methyl carbons (CMCs)- Disadvantage: Expensive

• Ammonia- Disadvantage(s): pungent, toxic, and flammable

• Hydrocarbons- Disadvantage(s): flammable

• Carbon Dioxide- Disadvantage: greenhouse gas

Global warmingGlobal warming

A green house effect and Global A green house effect and Global warmingwarming

Part 2

How does the Global worming take place??

When the solar radiation first fall on the top of the atmosphere the harmful UV radiations are absorbed by the O3. In this process some part of the UVs are reflected to the atmosphere and some are converted in to IF rays which is not lethal to man.

IF radiations coming to earth from the sun are of short wavelengths but the IF rays reflected from the earth are of long wavelengths. The IF radiation reflected from the earth cannot escape out from the carbon dioxide layer present in the atmosphere. CO2 gas has the ability to absorb IF radiation reflected from the earth surface.

The heating up of earth’s atmosphere due to trapping of IF rays; that has reflected from the earth surface by the CO2 layer (in the atmosphere) called Green house effect which caused global warming.

It has been observed that• CO2 (a GHG) can increase temperature by 50% .• CFCs can increase temperature by20%.• Other air pollutants can increase temperature by

30%

How does the Global worming take place??

Greenhouse gases

Greenhouse gases are made out of: – water vapor – carbon dioxide – methane – nitrous oxide – ozone – chlorofluorocarbons (CFCs)(halocarbons)

They are all natural gases, but extra greenhouses gases can be made from the anthropogenic activities.

GHGs influenced by human activities

Impacts of Global Warming

• Increase in the flow of rivers and change in rainfall pattern.

• Chances of submersion of islands.• Occurrence of more cyclones and hurricanes.• This will cause damage of agricultural crops.• Fresh water will be contaminated with the salty

water of sea.• Human population will be displaced.• The forest vegetation will not be able to adapt

with the changing temperature and may face destruction.

• As a result of global warming, the temperature of southern Europe and Central America will rise and affect the rain fall in these areas.

• Dobson Units (DU): The number of molecules required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0 degrees Celsius and an air pressure of 1 atmosphere (the pressure at the surface of the Earth).