CLEAN AIR - SELF STUDY
These exercises will guide you through the Fourth Year topic “Clean Air”.
This topic is covered in section C2f of your text book, beginning on page 59. Read this
chapter as you work through the exercises below.
Before you begin write the new topic title “CLEAN AIR” on a new page. If you are starting
this topic before finishing some other work, leave about three pages gap so that the other
work can be finished at a later date.
Do the following exercises in order. Begin each by writing the title of the exercise and
copying out the parts in bold at the start of each exercise. Then read and follow the
instructions.
EXERCISE 1 - What is in the air?
Air is a mixture of gases.
Your text book lists some of the most common gases in clean dry air. About 99% is
oxygen and nitrogen and almost all the rest is argon. All the other gases together make up
only 0.1% in total. This includes carbon dioxide (about 0.035 %); it is very important and is
often in the news but it is not a big component of air.
Follow this link [http://www.physlink.com/reference/AirComposition] to a website that lists
the top ten gases in air.
Write a table listing the percentages of the top ten gases and draw a pie chart, like that on
page 60 of your text book, to show the relative amounts of nitrogen, oxygen and others.
Why do you think books and websites usually list the percentage composition of dry air?
Write an answer, using full sentences, in your exercise book.
EXERCISE 2 - The origin of the atmosphere
Earth’s early atmosphere was very different from today’s.
When the Earth formed about 4½ billion years ago any free hydrogen and helium
drifted off into space and the first atmosphere would have been made up of gases
released by volcanoes; mostly steam and carbon dioxide with some ammonia and
methane.
None of these these gases are present in large quantities in today’s atmosphere. Where
did these gases go and where did today’s nitrogen and oxygen come from?
E A R L Y
A T M O S P H E R E
(from
NH3
ammonia
H2O
water
volcanoes)
CH4
methane
N2
nitrogen
CO2
carbon dioxide
O2
oxygen
C U R R E N T
A T M O S P H E R E
Draw a big, clear diagram based on the one above, to show what has happened to Earth’s
atmosphere over time. You might want to do it on a whole page, landscape format. Each
arrow
should have a
label
chosen
from
the
list below.
Use
your
textbook or
the
internet to
decide which label goes with which arrow. (There are 8 arrows and only 7 labels because
one of the labels can be used to describe two arrows at once.)
•
•
•
•
•
•
•
as Earth cools this condenses to form oceans
once green plants appear this is used up by photosynthesis to make oxygen gas
once oxygen has been produced this reacts to form more water and carbon dioxide
de-nitrifying bacteria convert this to nitrogen gas
once oceans form this dissolves in the oceans
once dissolved in oceans this can form sedimentary rocks like limestone or chalk
nitrifying bacteria convert this to nitrate minerals
EXERCISE 3 - Carbon dioxide and oxygen balance
Carbon dioxide and oxygen can be converted into one another by a number of
chemical processes. Without man’s interference these processes are roughly
balanced and the relative amount of oxygen and carbon dioxide in the atmosphere
does not change.
The main processes of conversion are illustrated in the diagram on page 60 of your text
book. Copy this diagram or create your own version and write a brief description of how
each process changes the relative amounts of carbon dioxide and oxygen.
Beneath this, write a brief explanation of how mankind is disturbing this natural balance;
use the three bullet points at the top of page 61 to help you.
The processes you have written about are part of a wider system called the carbon cycle
that includes all the different ways in which carbon is recycled in the natural world. Many
great illustrations of this can be easily found on the internet by searching Google Images
for “carbon cycle”. Find one you like and understand and either print it out and stick it in or
use it as a basis from which to draw your own version.
Why is there so much international concern about recent increases in the amount of
atmospheric carbon dioxide? Write a short paragraph about the consequences of
increased levels of carbon dioxide.EXERCISE
4 - Atmospheric pollution
Air includes small quantities of pollutants; damaging substances that have been
produced by human activities. Some of the most important are oxides of nitrogen
(mostly nitrogen dioxide NO2 but also nitrogen monoxide NO), sulphur dioxide (SO2)
and carbon monoxide (CO).
Copy the table from the middle of page 59 of your textbook. It summarises how these
pollutants form and what effect they have.
Now look the following table. It lists the total mass of NO2 produced annually in the UK
over the period 1970 to 2005. It also sub-divides this total to show how it was produced.
Table 1 : Mass of NO2 / thousand tonnes
1970
1975
1980
1985
1990
1995
2000
2005
Transport
770
890
990
1140
1320
1070
820
550
Power
stations
1330
910
940
830
850
480
420
460
Other
1030
800
840
840
790
690
660
610
Total
3130
2600
2770
2810
2960
2240
1900
1620
This data can be used to create the following graph:
Graph 1 : Amounts of NO2 produced 1970 - 2005
Either print and stick this graph in to your book or make your own version using excel or
graph paper and pencil.
Now use the following two tables to create similar graphs showing changes in amounts of
SO2 and CO. Make sure they are clearly labelled, just like the graph above. Stick these
into your book as well.
Table 2 : Mass of SO2 / million tonnes
1970
1975
1980
1985
1990
1995
2000
2005
Power
stations
3730
3510
3460
2830
2930
1750
870
450
Others
2640
1690
1320
890
790
600
330
240
Total
6370
5200
4780
3720
3720
2350
1200
690
Table 3 : Mass of CO / thousand tonnes
1970
1975
1980
1985
1990
1995
2000
2005
Transport
5350
5320
5390
5200
5480
4180
2500
1120
Residential
4500
2730
2150
2020
1190
850
630
330
Other
2270
1830
1610
1610
1560
1270
1100
930
Total
1970
1975
1980
1985
1990
1995
2000
2005
12120
9880
9140
8840
8230
6300
4230
2390
EXERCISE 5 - The catalytic converter
Car and lorry engines are responsible for a lot of NOx and CO pollution. The
amounts of these gases have decreased over recent years due to widespread use of
catalytic converters in car exhaust systems.
Read the section at the bottom of page 61 and write a brief description of what a catalytic
converter does. Include both the word and symbol equation for the overall process.
A metal catalyst must be used to make the reaction happen quickly as the gases
pass through the exhaust system in less than one tenth of a second.
Your book simplifies how a converter works; in reality the conversion of NO to N 2 occurs
before CO is converted to CO2, often in a different part of the converter. At the same time,
unused fuel vapour is also converted to carbon dioxide and water.
Go to youtube.com and search for “catalytic converter deconstructed” and you should find
that the first hit is a four and a half minute video from an American science channel.
Use the video to answer these questions in full sentences in your exercise book:
1. Which three precious metals are used in catalytic converters?
2. How big is the surface area within one catalytic converter?
3. Why does the surface area need to be so large?
4. Why are catalytic converters ineffective during the first part of a journey?
5. How far does a car need to travel before the converter becomes effective?
EXERCISE 6 - End of topic questions
Read the passage on page 62 of your text book and answer the comprehension questions
in your exercise book in full sentences.
Now turn to page 72 of your text book and try to answer all the end of topic questions 1 – 6
in section C2f.
Gateway sheet?