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The Ozone Layer

A Quick presentation on the Ozone Layer

Daniel Cooper

on 29 March 2011

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Transcript of The Ozone Layer

The Ozone Layer Objectives of Today's Lesson Explain that Ozone is continuously being formed and broken down in the stratosphere by ultraviolet radiation. Describe, using equilibrium, how the ozone concentration is maintained in the ozone layer, including the role of UV radiation. Outline the role of ozone in the absorption of harmful UV radiation & the resulting benefit for life on Earth. What Is The Ozone Layer? The ozone layer is a layer in the atmosphere which contains high concentrations of Ozone (O3).
Ozone is actually split into two parts of the atmosphere
The Troposphere, which is the closest region to Earth and contains about 10% of all ozone.
The Stratosphere contains the other 90%. This layer absorbs 97-99% of the sun’s Highest frequency Ultraviolet Light, which is damaging to life on Earth and is located in the lower portion of the stratosphere from approximately 8.1 to 25 miles above Earth but the thickness varies seasonally and geographically. It was discovered by two French physicists called Charles Fabry and Henri Buisson in 1913.
Most of our understanding about the ozone layer is thanks to British meteorologist G.M.B. Dobson. He devoted most of his life to the observation & study of atmospheric ozone and developed a simple spectrophotometer to measure stratospheric ozone from the ground. Between 1928 and 1958, Dobson set up a worldwide network of ozone monitoring stations which are still in use today. ozone concentration is measured in units called Dobsons, in his honour. Ozone: Good or Bad? Ozone consists of three oxygen atoms.

Environmentally, ozone can be both bad and good, depending where it is found.
And now for the science.. Bad: Good: Ozone near to the Earth's surface in the troposphere is an air pollutant with harmful effects on the respiratory systems of animals. Ozone in the upper atmosphere in the stratosphere protects living organisms by preventing harmful UV Light from reaching the Earth's surface. The Ozone-Oxygen Cycle Ozone is continuously being formed and broken down in the stratosphere by the action of UV radiation.

There are three different types of UV radiation based on the wavelength:
UV-a (320-400 nm)- reaches the Earth's surface, it has less energy than the shorter wavelengths and is not as damaging. UV-a radiation isn't considered to be a massive concern. UV-b (280-320 nm) - radiation can cause sunburn, sometimes genetic damage and can cause skin cancer if prolonged exposure occurs. UV-c (200-280 nm) - is entirely screened out by the ozone layer. Although ozone screens out MOST UV-b, some does reach the Earth's surface. Any decrease in the ozone layer would allow more UV-b radiation to reach the surface, causing increased genetic damage to living organisms. The formation of Ozone The first step in the formation of ozone is the absorption of UV radiation with a wavelength less than 240 nm by O2 Molecules. This is high-energy radiation, capable of making an O2 molecule into two oxygen atoms. O2 + (radiation < 240 nm = 2O The O atoms then react with O2 molecules to form ozone molecules, O3. This process generates Heat. O2 + O = O3 + Heat What is ozone and where is it in the atmosphere?

Ozone is a gas that is naturally present in our atmosphere. Each ozone molecule contains three atoms of oxygen and is
denoted chemically as O3.
Ozone is found in two regions of the atmosphere.
About 10% of atmospheric ozone is in the troposphere, the region closest to Earth.
The remaining ozone (90%) resides in the stratosphere, between the top of the troposphere and about 50 kilometers
The large amount of ozone in the stratosphere is often referred to as the “ozone layer.” How is ozone formed in the atmosphere?

Ozone is formed throughout the atmosphere in multistep chemical processes that require sunlight. In the stratosphere,
the process begins with an oxygen molecule (O2 ) being broken apart by ultraviolet radiation from the Sun.

In the lower atmosphere (troposphere), ozone is formed in a different set of chemical reactions
involving hydrocarbons and nitrogen-containing gases. Why do we care about atmospheric ozone?

Ozone in the stratosphere absorbs some of the Sun’s biologically harmful ultraviolet radiation.
Because of this, stratospheric ozone is considered “good” ozone.
In contrast, excess ozone at Earth’s surface that is formed from pollutants is considered “bad” ozone because it can be harmful to humans, plants, and animals.
The ozone that occurs naturally near the surface and in the lower atmosphere is also beneficial because ozone
helps remove pollutants from the atmosphere. How is ozone measured in the atmosphere?

The amount of ozone in the atmosphere is measured by instruments on the ground and carried aloft on
balloons, aircraft, and satellites.
Some measurements involve drawing air into an instrument that contains
a system for detecting ozone.
Other measurements are based on ozone’s unique absorption of light
in the atmosphere.
In that case, sunlight or laser light is carefully measured after passing through a portion
of the atmosphere containing ozone.
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