Science Presentation

Ozone Layer Depletion &

Greenhouse effect

The Ozone Layer

And Ozone Holes

What is Ozone? A molecule containing three

atoms of oxygen is called ozone. Ozone is very rare in our atmosphere, averaging about three molecules of ozone for every 10 million air molecules. In spite of this small amount, ozone plays a vital role in the atmosphere.

Where is ozone found in the atmosphere?

Ozone is mainly found in two regions of the Earth's atmosphere. Most ozone (about 90%) resides in a layer that begins between 6 and 10 miles (10 and 17 kilometers) above the Earth's surface and extends up to about 30 miles (50 kilometers). This region of the atmosphere is called the stratosphere. The ozone in this region is commonly known as the ozone layer.

What is the role of the ozone layer and how are humans affected by it?

Ozone present in the stratosphere plays a beneficial role by absorbing most of the biologically damaging ultraviolet sunlight. The absorption of ultraviolet radiation by ozone creates a source of heat. Ozone thus plays a key role in the temperature structure of the Earth's atmosphere.

Without the filtering action of the ozone layer, more of the Sun's UV radiation would penetrate the atmosphere and would reach the Earth's surface. Many experimental studies of plants and animals and clinical studies of humans have shown the harmful effects of excessive exposure to UV radiation.

At the Earth's surface, ozone comes into direct contact with life-forms and displays its destructive side (hence, it is often called "bad ozone"). Because ozone reacts strongly with other molecules, high levels of ozone are toxic to living systems. Several studies have documented the harmful effects of ozone on crop production, forest growth, and human health. The substantial negative effects of surface-level ozone present in the troposphere from direct toxicity contrast with the benefits of the additional filtering of UV radiation that it provides.

There is also widespread scientific and public interest and concern about losses of ozone in the stratosphere. Ground-based and satellite instruments have measured decreases in the amount of stratospheric ozone in our atmosphere. Over some parts of Antarctica, up to 60% of the total overhead amount of ozone (known as the column ozone) is depleted during Antarctic spring (September-November). This phenomenon is known as the Antarctic ozone hole. In the Arctic polar regions, similar processes occur that have also led to the depletion of column ozone.

What is the ozone hole?      The ozone hole is an annual thinning of

the ozone layer over Antarctica. The most pronounced decrease in ozone has been in the lower stratosphere. However, the ozone hole is most usually measured not in terms of ozone concentrations at these levels (which are typically of a few parts per million) but by reduction in the total column ozone.

 

The Antarctic Ozone Hole

The Ozone hole as seen from the

Earth

What causes Ozone Holes?    The cause of the ozone holes is generally

agreed to be CFC (chlorofluorocarbon) compounds which break down due to ultraviolet light and become free radicals containing chlorine high in the Earth's atmosphere. These radicals then break down the ozone catalytically. The ozone layer can also be depleted by free radical catalysts, including nitric oxide (NO), nitrous oxide (N2O), hydroxyl(OH), atomic chlorine (Cl), and atomic bromine (Br).

What are CFC’s ? A chlorofluorocarbon (CFC) is an organic

compound that contains only carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. Chlorofluorocarbons (CFCs) are anthropogenic compounds that have been released into the atmosphere since the 1930s in various applications such as in air-conditioning, refrigeration, blowing agents in foams, insulations and packing materials, propellants in aerosol cans, and as solvents.

What actions have been taken to protect the ozone layer?

Through an international agreement known as the Montreal Protocol on Substances that Deplete the Ozone Layer, governments have decided to eventually discontinue production of CFCs, halons, carbon tetrachloride, and methyl chloroform (except for a few special uses), and industry has developed more "ozone-friendly" substitutes. All other things being equal, and with adherence to the international agreements, the ozone layer is expected to recover over the next 50 years or so.

The Greenhouse Effect

Greenhouse GasesGreenhouse gases are those gases in the

atmosphere that absorbs and emits radiations

within a thermal infra-red range. The primary

greenhouse gases in the Earth's atmosphere are

water vapor, carbon dioxide, methane, nitrous

oxide, and ozone.

The Greenhouse EffectThe greenhouse effect is the process in

which greenhouse gases absorbs radiation

(the infra red rays) and re- radiates it in all

directions. Since part of this re-radiation is back

towards the surface and the lower atmosphere,

it results in an elevation of the average surface temperature above what it would be in

the absence of the gases.

CO2CO2

CO2

CO2

CO2

CO2

CO2

CO2

CO2

CO2

co2

CO2

Why is this effect named after a greenhouse?

A greenhouse is a structural building with different types of covering materials, such as a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming visible sunshine is absorbed inside the structure. Air warmed by the heat from warmed interior surfaces is retained in the building by the roof and wall; the air that is warmed near the ground is prevented from rising indefinitely and flowing away. This  process in which the heat is trapped within the greenhouse can be compared to the  way in which the heat radiations are trapped in the earth’s atmosphere.

how to reduce greenhouse effect?Green house effect is something that cannot be

prevented but can be reduced. It can be reduced in the following ways:1. By opting for greener technologies that are eco-

friendly. 2. By reducing emissions from automobiles, the

greenhouse gases can be reduced. 3. By preventing deforestation, because plants absorb

a great amount of CO2 from the atmosphere. 4. By using CFC-free refrigerators.5. By reducing use of aerosols because they produce

CFCs.

Global Warming Global warming refers to an unequivocal

and continuing rise in the average temperature of Earth's climate system. Most of global warming is being caused by increasing concentrations of greenhouse gases produced by human activities. Future climate change and associated impacts caused by global warming will vary from region to region around the globe. Global warming can be prevented by reducing the emission of greenhouse gases.

Effects of Global Warming• Increase in spread of disease.• Warmer waters and more hurricanes.• Increase in droughts and heat waves.• Economic consequences.• Melting of polar ice caps.• Floods.• Fires and wildfires.• Storms.• Death by smog.• Desertification.• Tsunamis.• Cold waves.• Increase in volcanic activities.• Loss of biodiversity and animal extinction.

Melting and breaking down of polar ice caps.

Artist’s illusion of New York city underwater. 

Artist’s illusion of backwards evolution in case of polar bears.

THAT’S ALL FOLKS!!