Llantwit Major School
October 2011
C1 Air Quality
Revision Notes
1) The Atmosphere
The atmosphere is made up of a mixture of gases which are small molecules with large
spaces between them. The main gases are:




Nitrogen 78%
Oxygen 21%
Argon 1%
Small amounts of other gases e.g. carbon dioxide
(0.037%) and water vapour
2) Evolution of the Atmosphere
The early atmosphere would have been made of mainly carbon dioxide and water vapour
released by volcanic eruptions and volcanic activity. As the earth cooled the water vapour
condensed and formed the oceans. The evolution of photosynthesising organisms caused
the production of oxygen and the reduction of carbon dioxide. Carbon dioxide also dissolved
in the oceans, which was used by organisms in the sea to create their shells. These shells
were converted into sedimentary rock over millions of years and eventually turned into
fossil fuels. These processes produced the atmosphere as we know it today.
3) Air Pollutants
The major air pollutants are:
Pollutant
Carbon dioxide
Formula
CO2
Particle diagram
Produced by…
Problem
The combustion Causes global
of coal and fuels warming
(i.e.
hydrocarbons)
Llantwit Major School
October 2011
Carbon
monoxide
CO
Carbon
particulates
C
Sulfur dioxide
SO2
Nitrogen
dioxide
NO2
Incomplete
Poisonous
to
combustion of humans
by
coal and fuels
stopping
the
red blood cells
carrying oxygen
Incomplete
Linked
to
combustion of asthma
and
coals and fuels
global dimming.
Cover buildings
with soot
Combustion of Causes acid rain
coal and fuel by dissolving in
containing
rain clouds
impurities
of
sulfur
Combustion of Causes acid rain
nitrogen in car by dissolving in
engines
rain clouds
produces
nitrogen
monoxide which
is oxidised in the
atmosphere to
form nitrogen
dioxide
4) Combustion of Coal:
Coal is made up mainly of carbon. Coal is often burnt in power stations and the energy given
off is used to make electricity. When coal burns (combusts) it reacts with oxygen in the air to
produce carbon dioxide. The chemical equation for this is:
Carbon
+
Oxygen

Carbon dioxide
The substances reacting together are the reactants (i.e. carbon and oxygen) and the
substance produced is the product (i.e. carbon dioxide). A chemical reaction where a
substance combines with oxygen is called oxidation. Combustion is an example of oxidation.
Coal burns more rapidly in pure oxygen than in the air.
Llantwit Major School
October 2011
If there isn’t enough oxygen present incomplete combustion occurs. The products of
incomplete combustion are carbon monoxide or carbon particulates:
Notice that the number of atoms of each element on the left hand side of the reaction (the
reactants) is the same as the number of atoms of each element on the right-hand side of the
reaction (the products). This is called conserving mass.
5) Combustion of Hydrocarbon fuels
Most fuels are made up of hydrocarbons, for example petrol, natural gas (methane) and
diesel. Hydrocarbons are compounds containing only hydrogen and carbon atoms. When
hydrocarbons combust (i.e. react with oxygen in the air) carbon dioxide and water are
produced. The carbon in the hydrocarbon fuel reacts with oxygen to form carbon dioxide
and the hydrogen in the hydrocarbon fuel reacts with oxygen to form water. The chemical
equation for the combustion of methane would be:
+
+
Notice that the number of atoms of each element is that same on both sides of the equation
(conserving mass). If there wasn’t enough oxygen present carbon monoxide or carbon
particulates could be formed instead of carbon dioxide (incomplete combustion).
6) Production of other pollutants
Sulfur is found as an impurity in coal and hydrocarbon fuels. When coal and other fuels are
burnt, sulfur is able to react with oxygen forming sulfur dioxide. The chemical equation is:
Llantwit Major School
October 2011
In car engines, air is drawn in from the atmosphere which provides oxygen for the
combustion of petrol or diesel. At the high temperatures found in car engines nitrogen from
the air is able to react with oxygen to form nitrogen oxide. Nitrogen oxide is released into
the atmosphere which is oxidised. This means it reacts with oxygen in the air to form
nitrogen dioxide. Nitrogen dioxide is able to react with water and oxygen to form acid rain
which damages trees and crops.
7) Reducing Air Pollution
a) Reducing pollution from burning coal
The amount of polluting gases produced by power stations that burn fossil fuels can be
reduced by:




Using less electricity so that less fossil fuels are burnt and therefore less carbon
dioxide and other harmful gases are produced.
Removing sulfur from natural gas and fuel oil which prevents sulfur dioxide being
produced when they are burnt
Removing sulfur dioxide from flue gases by wet scrubbing: an alkaline slurry (made
of calcium oxide and water) or sea water is sprayed onto the waste gases causing the
sulfur dioxide to be neutralised and preventing the release of sulfur dioxide into the
atmosphere
Removing carbon particulate from flue gases preventing the release of carbon
particulate which land on surfaces (e.g. of buildings) making them dirty
Llantwit Major School
October 2011
b) Reducing pollution from car exhausts
Various pollutants are produced from the combustion of fuels in cars (carbon dioxide, sulfur
dioxide and nitrogen oxide). There are a number of ways of reducing these emissions:






Having more efficient engines which burn less fuels
Using low sulfur fuels
Using more public transport, or walking and cycling instead of driving
Having legal limits on exhaust emissions (tested during the MOT of cars)
Using biofuels or electric vehicles (you should be aware there are benefits and
problems to using alternative fuels. For example biofuels are produced by growing
large amounts of crops which means the land is not able to be used to grow food,
however they are carbon neutral. Electric vehicles still produce emissions as the
majority of electricity is produce from fossil-fuel burning power stations).
Using catalytic convertors: catalytic convertors are found in car exhausts. They
convert carbon monoxide into carbon dioxide by reacting the carbon monoxide with
oxygen (oxidation). They also reduce nitrogen monoxide by converting it into
nitrogen and oxygen.
The only way of reducing carbon dioxide from both cars and power stations is to burn less
fossil fuels.
8) Analysing data about air pollution
You must be able to (the bold lettering summaries what you need to know, the lettering in
italics gives examples and further explanation):



Use data to back up (justify) an explanation: E.g. “I know that Car A is better for the
environment because the data shows that it produces less carbon dioxide emissions
that car B”.
Explain why it is important to repeat results (reproducibility (you can repeat your
own results in multiple tests) and repeatability (that someone else can repeat your
results) and give reasons why, if you were to perform only 1 test, the results may
not be the true value: E.g. You perform a test by a busy main road to measure air
pollution in one area by collecting soot particles on a square of sticky paper. You find
that you do not collect any air pollution which seems strange as it is next to a busy
road. You repeat the test using multiple squares of paper and find that on average 20
carbon particulates are found in each square. You discover that the first time you
performed the test water had dropped onto the sticky paper washing the pollution
away.
Calculate the mean of a set of data and state that the mean is the best estimate of
the true value.
Llantwit Major School
October 2011



Understand that by repeating a test you can identify the range of your data and
explain that the true value is likely to fall within that range. E.g. the emissions of
nitrogen oxide from a car exhaust is measured 5 times. The mean is found to be
33ppm and the range 30-35ppm. The actual amount of nitrogen oxide released from
the car (the true value) is very likely to be within your range and your best estimate
of the actual amount is your calculated mean. The reason you cannot measure the
exact amount every time will be due to errors in your measuring equipment and
because of the procedure itself (i.e. the way go about measuring them).
Identify outliers and explain your decision to discard them from your results: you
should recognise that an outlier lies well outside your range and is very different to
the other results. You may be asked to explain why an outlier for a particular set of
data has occurred.
Discuss if there is a real difference between 2 sets of data: there is only a real
difference if the ranges do not overlap
9) Correlation and cause
You need to recognise that there may be a correlation between 2 sets of data. For example
during the summer ice cream sales increase and hay fever cases increase. However, one
does not necessarily cause the other. This means that whilst there may be a correlation
between 2 sets of data (e.g. hay fever and ice cream sales), one may not cause the other
(i.e. eating ice cream does not cause hay fever). When looking at correlations you need to
try and find out if there is a link between the two, for example if you look at the graph you
will see there is a correlation between smoking and getting lung cancer. This correlation was
spotted in the 1975, however it wasn’t until years later that the link between the two was
found and a mechanism was determined to explain how smoking causes lung cancer.
Llantwit Major School
October 2011