Chemistry Module C1: Air Quality

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The Atmosphere

The atmosphere is a thin

layer of gases around the Earth made up from…

• 78% nitrogen

• 21% oxygen

• 1% argon

• Small amounts of water vapour, carbon

dioxide and other gases.

Scientists believe it formed due to large amounts of

volcanic activity on Earth a long time ago, therefore the atmosphere was mostly

carbon dioxide and water vapour. Eventually the Earth cooled and water vapour

became our oceans, allowing microscopic organisms to form which produced oxygen

and removed carbon dioxide.

What the Earth might have looked like during volcanic activity which produced large amounts of carbon dioxide and water vapour.

Pollutants

Pollutants are chemicals which damage the environment and,

indirectly, humans. Pollutants can be formed when we burn fossil fuels such as

in our cars, and power stations. Other examples of pollutants are…

• Carbon

dioxide – traps heat in the Earth’s atmosphere (a greenhouse gas)

• Nitrogen

oxides – causes acid rain, creates breathing problems

• Sulphur

dioxide – causes acid rain

• Carbon

monoxide – prevents blood from carrying oxygen

• Particulates

– makes things dirty, creates breathing problems

Pollutants cannot just disappear from the atmosphere, they

have to go somewhere. This is where problems start occurring. Particulate

carbon is deposited on surfaces such as stone building which make them dirty.

Carbon dioxide stops heat from leaving the atmosphere, which contributes to

global warming. Sulphur dioxide and nitrogen dioxide cause acid rain after

reacting with water. Acid rain damages trees, corrodes metals and upsets the pH

level of rivers which causes animals and plants to die.

A dirty van, caused by particulates from incomplete combustion/

Chemicals

Elements are the ‘building blocks’

of everything, each is made up from the structure of tiny particles called

atoms. Compounds are where elements chemically combine to form a new substance.

For example, H2O is formed when 2 hydrogen (H) elements combine with

an oxygen (O) atom. Like Hydrogen and Oxygen, each element has its own chemical

symbol which is recognised worldwide. Reactions in these formulae can

completely change the atom structure, depending on whether they separate or join

other atoms, or even do both. Changes are usually not reversible. No atoms are

lost or created in a reaction, so the mass stays the same. The mass is

conversed.

Combinations

like H2O are shown in equations with an arrow from the reactants

(starting substances) to the products. There are word equations which clearly

show what has reacted and what the products are and there are formula equations

which show more depth into why it happens. There will always be the same number

of atoms on both sides of the equation because none are lost and none are

created.

H + O > 2H O

2

2

2

A simple balanced equation for hydrogen reacting with oxygen to produce water.

Combustion

Combustion (burning) is a

reaction between a fuel and oxygen that creates energy, such as coal and

oxygen. Oxygen usually comes from the air, but pure oxygen will give a faster

reaction. Coal is mostly carbon, so when one atom of carbon reacts with an atom

of oxygen it creates CO2.

There are two types of

combustion, complete and incomplete. Complete is when there is plenty of oxygen

for the fuel to completely burn. Hydrocarbons are formed from these reactions,

which are mainly carbon and hydrogen. They produce carbon dioxide and water

vapour only when burned in the air.

Incomplete combustion occurs when

there is not enough oxygen for all of the fuel to burn. It results in carbon

particulates or carbon monoxide being produced. Incomplete combustion most

commonly occurs in car engines; hence the exhaust is needed to remove

particulates and other dangerous chemicals which have been created.

High temperatures, such as that of a car

engine, can cause oxygen and nitrogen to react which produced nitrogen monoxide

(NO). This is then oxidised to produce nitrogen dioxide (NO2). When

they occur together, they’re called NOx.

Combustion

Reducing Pollution

Some Carbon Dioxide is removed by photosynthesis in plants

and by dissolving in water. However, we produce too much carbon dioxide and cut

down trees etc. so the levels of it rise each year.

In power stations, emissions are reduced by, simply, using

less electricity. Also, sulphur and other toxic chemicals are removed from

coal, gas and oil before combustion. Sulphur dioxide can be removed from a

chimney of a power station with a process called wet scrubbing with a spray of

calcium oxide and water, or seawater. Alternatively, we should start using

renewable energy sources more such as solar, wind and hydroelectricity.

Around half of the UK’s carbon monoxide emissions come from

road transport. Emissions can be reduced by…

• Using

low-sulphur fuel in cars with new, efficient engines

• Legal

limits for exhaust emissions, tested for during MOT tests

• Installing

catalytic converters in cars to reduce toxic gas emissions

• Using

public transport

Catalytic converters replace hazardous gases such as carbon

monoxide and nitrogen monoxide with nitrogen and carbon dioxide by reacting

them with oxygen. Electricity is an alternative way to power cars, so long as

it is renewable. Biofuels could also be a solution, but it takes up lots of

valuable farmland.

Simply though, the only way to reduce emissions is to burn

less fossil fuels. This is becoming more difficult as the ever-growing world

population demands more electricity.

Think you know it all now?

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The Atmosphere

Pollutants

Chemicals

Combustion

Reducing Pollution