Atmosphere

Atmosphere

CompositionOzone LayerHuman Impact

Our Atmosphere

Is fixed – i.e. closed system for matter, but not energy!

Has many functions– Protection from cosmic rays– Keeping us warm– Oxygen

Its all relative

Is a very thin layer of gas

Is small compared to Earth itself

Composition & Layers

Troposphere

The lowest layer– Home of life– Home of weather– Home of pollution – mainly from human impact

Sources of pollution

Humans – industry, transport and domestic– Is particulate (carbon, dust and metals) and

gaseous (carbon dioxide, smog, unburnt hydrocarbons, etc.

Can be natural – Chief source is volcanic activity

Stratosphere

Home of the ozone layer Where the Concorde once flew Where global warming originates

What is ozone

Allotrope of oxygen Formed naturally Oxygen molecule split

by UV radiation Unstable Oxygen atom

forms Atom joins with

molecule to form ozone

O2 + UV O + O

Spliting of the oxygen molecule by UV light. The oxygen atoms formed are not stable and quickly "attack" other oxygen molecules to form ozone molecules.

O + O2 O3

The oxygen free radical

This is another name for the unstable oxygen atom

contains an unpaired electron in its outermost shell of electrons. – This is an extremely unstable configuration, – radicals quickly react with other molecules or

radicals to achieve the stable configuration of 4 pairs of electrons in their outermost shell

How can Ozone be stable?

Simply put, a special bond forms It is called a co-ordinate covalent bond One of the oxygen molecule atoms has to

share two electrons with the atom!

How the bond forms

O O O

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x x

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The oxygen molecule has a double bond. These 4 electrons are shared so that each atom has the "magic 8"

These two electrons are shared by the molecule with the atom. This also means that both atoms have access to 8 electrons.

Decomposing ozone

Ozone is readily split apart to form oxygen molecules This is a natural process occurring in the atmosphere

O3 + O 2 O2

CFC’s the real villains!

CFC = chloro fluoro carbons CFCs were developed in the early 1930s and are

used in a variety of industrial, commercial, and household applications

Used as coolants for commercial and home refrigeration units, aerosol propellants, electronic cleaning solvents, and blowing agents

Halons are also to blame

Are compounds of bromine, fluorine and carbon

The halons are used as fire extinguishing agents, both in built-in systems and in handheld portable fire extinguishers

CFC and ozone

In 1973 chlorine was found to be a catalytic agent in ozone destruction

It essentially cleaves the ozone to produce oxygen molecules – see decomposing ozone

The chemistry – we think

O3 + Cl O2 + ClO

ClO + O O2 + Cl

As we see, the chlorine atom is used and produced by the reaction. This is similar to recycling chemicals in a reaction - the net result is the reaction is self-perpetuating.

Simply put

1. Human activity puts chlorides and bromides into the atmosphere.

2. Cold conditions are present in the Polar Regions that allow the accumulation of the CFC’s.

3. Sunlight breaks down the CFC’s. 4. Under certain conditions atomic chlorine forms and

this has a major part in the breakdown of ozone.5. The breakdown products destroy ozone.6. The ozone is broken into oxygen molecules.7. No more Ozone protection in the stratosphere.

So what’s being done

The CFC problem may be hard to solve because there are already great quantities of CFCs in the environment. 

CFCs would remain in the stratosphere for another 100 years even if none were ever produced again

In the Montreal Protocol, 30 nations worldwide agreed to reduce usage of CFCs and encouraged other countries to do so as well

Montreal Protocol

The governments of the world got together to try to stop the problems that were clearly evident – the major push was the gradual phasing out of CFC’s.

The Montreal Protocol was a convention signed in 1987 by many countries to greatly reduce the production and use of CFCs which had been shown to be responsible for damage to the ozone layer.

Since 1987, further amendments to the protocol have imposed even greater restrictions of the production and use of potentially damaging compounds.

What’s it mean to me?

Small steps are being taken to reduce CFCs including the use of alternate propellants in:

Refrigeration units Air conditioning units Propellants for spray cans Using pump action instead of gas propellants

But surely there are alternatives!

You bet! In place of CFCs and Halons we now use:

Two CFC replacements have been developed for medical uses; they are referred to as hydrofluoroalkanes (HFAs) or as hydrofluorocarbons (HFCs), and contain only carbon, hydrogen and fluorine.

They are non-flammable and chlorine-free, so they have no impact on the stratospheric ozone layer.

Being more specific

Cyclopentane and cyclohexane have been put forth as replacements for coolants

Nitrogen gas can be used as a blowing agent

C C

CC

CH

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H H

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C C

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CC

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cyclopentane

cyclohexane