AirAirAirAir

OverviewOverviewOverviewOverview

Our atmosphere has been taken for granted in the past. In the last few decades, scientists and the general public began to realise the adverse effects of pollutants on the air we breathe. It is now recognised that pollutants such as sulfur dioxide, oxides of nitrogen, and particulates released into the atmosphere as a result of energy generation and increased use of motor vehicles, have serious health and environmental consequences.

In this section, the sources of air pollutants and their effects are examined. Students should be able to value the knowledge of the hazardous nature of pollutants and the environmental issues related to air pollution.

Course SyllabusAt the end of this chapter, you should be

able to:

a. describe the volume composition of gases present in dry air as 79% nitrogen, 20% oxygen and the remainder being noble gases (with argon as the main constituent) and carbon dioxide

b. name some common atmospheric pollutants e.g. carbon monoxide; methane; nitrogen oxides (NO and NO2); ozone; sulfur dioxide; unburned hydrocarbons

Course SyllabusAt the end of this chapter, you should be

able to:c. state the sources of these pollutants as

– carbon monoxide from incomplete combustion of carbon-containing substances

– nitrogen oxides from lightning activity and internal combustion engines

– sulfur dioxide from volcanoes and combustion of fossil fuels

Course SyllabusAt the end of this chapter, you should be

able to:d. discuss some of the effects of these

pollutants on health and the environment– the poisonous nature of carbon monoxide– the role of nitrogen dioxide and sulfur

dioxide in the formation of “acid rain” and – its effects on respiration and buildings

Why is air important to us??

Feb 20, 2005

FIFTY FIREFIGHTERS STRUGGLED AGAINST THE WIND to bring the blaze in a forested area under control by 7pm but several pockets of fire remained because it was so windy. No one was injured. - ASHLEIGH SIM

http://straitstimes.asia1.com.sg/sub/latest/story/0,5562,302121,00.html?

Firemen have been putting out an average of about six bush fires a day since January due to the heat. - SEAN TAN

Feb 19, 2005

23 Sept, 1997 22 Sept, 1997 18 Sept, 1997

17 Sept, 1997 14 Sept, 1997 12 Sept, 1997

http://mrdata.com/~blakef/galleries/SingaporeHaze/haze.html

Good air is important for health.

Harm caused by haze:

• Breathing problems, particularly for people with asthma

• Interference with aircraft landings due to poor visibility, some airlines had to delay or cancel their flights

• Tourism industry suffers as visitors stay away.

“So, what air consists of?”

composition of air composition of airAir is a mixture of gases.Air is a mixture of gases.

argon (1%)oxygen

(20%)

nitrogen (79%)

contains 79% nitrogen

contains 20% oxygen

contains 1% other gases (including argon, carbon dioxide and water vapour)

contains 79% nitrogen

contains 20% oxygen

contains 1% other gases (including argon, carbon dioxide and water vapour)

Check this out!http://sunshine.chpc.utah.edu/labs/atmosphere/atm_gases1.html

What happens when things burn?

Elements combined with oxygen to produce oxides.

• C + O2 CO2

• 2Cu + O2 2CuO

• 2H2 + O2 2H2O

• 2Mg + O2 2MgO

• S + O2 SO2

oxygen

combustion is a reaction in which substances react with oxygen in an exothermic reaction

burning happens when flames are given out during combustion

combustioncombustionOxygen is obtained from air. It is compressed and stored in cylinders or kept as liquid in insulated tanks.

Some amount of oxygen can be produced in the laboratory through the decomposition of hydrogen peroxide.

oxygen

products of combustion are oxides examples:

ElementElement What is What is ObservedObserved

Appearance Appearance of Productof Product

Name and Name and Formula of Formula of

ProductProduct

carbonsolid burns with bright red glow

colourless gas with no

smell

carbon dioxide, CO2

copperpowder burns with

dull red glowblack solid

copper(II) oxide, CuO

hydrogenexplosion and flash of light

colourless liquid

water, H2O

magnesiumburns with very

bright white lightwhite solid

magnesium oxide, MgO

sulfurburns with blue

flame

colourless gas with

strong smell

sulfur dioxide, SO2

combustioncombustion

Fuels are burnt to provide energy.

Examples of fuels are compounds like hydrocarbon.

Hydrocarbons are simply compounds containing hydrogen and carbon.

The products formed from the combustion of hydrocarbons depend on certain conditions.

If there is sufficient oxygen, there will be complete combustion, producing carbon dioxide and water.

combustioncombustionoxygen

To show that carbon dioxide and water are produced when a candle burns in air.

hydrocarbon

Hydrocarbon + oxygen

carbon dioxide + water vapour

To show that carbon dioxide and water are produced when a candle burns in air.

Hydrocarbon + oxygen

carbon dioxide + water vapour

oxygenincomplete combustionincomplete combustion

occurs when combustion of hydrocarbons is incomplete due to lack of oxygen

produces two other substances: soot and carbon monoxide

effects of incomplete combustion can be seen in the laboratory Bunsen burner

occurs when combustion of hydrocarbons is incomplete due to lack of oxygen

produces two other substances: soot and carbon monoxide

effects of incomplete combustion can be seen in the laboratory Bunsen burner

complete combustion

air-hole opened(complete combustion)

pale blue (gas burning completely)

blue (unburnt gas)

air-hole closed(incomplete combustion)

yellow flame due to hot specks of unburnt carbon

incomplete combustion

Combustion without enough oxygen

Which Bunsen burner has the air valve open?Which Bunsen burner has less oxygen

available to react with the fuel - methane?

What two products are normally formed

during the combustion of a fuel?

A B

oxygen

comparing complete combustion and incomplete combustion of hydrocarbons:

comparing complete combustion and incomplete combustion of hydrocarbons:

Complete Complete CombustionCombustion

Incomplete Incomplete CombustionCombustion

products are CO2 and H2Oproducts include soot (C) and

carbon monoxide (CO)

plenty of oxygen to burn shortage of oxygen to burn

example: flame of a bunsen burner with air-hole opened

example: flame of a bunsen burner with air-hole closed

complete & incomplete combustioncomplete & incomplete combustion

Combustion is rarely complete when carbon compounds burn in air and carbon monoxide and soot produced can cause air pollution.Combustion is rarely complete when carbon compounds burn in air and carbon monoxide and soot produced can cause air pollution.

Do you know…Do you know…

People have been burning candles for People have been burning candles for thousands of years. Unknown to them, the soot thousands of years. Unknown to them, the soot produced contains tiny football-shaped produced contains tiny football-shaped molecules of carbon, each with 60 carbon molecules of carbon, each with 60 carbon atoms, and also a few rugby-ball-shaped atoms, and also a few rugby-ball-shaped molecules with 70 carbon atoms. It is a new molecules with 70 carbon atoms. It is a new form of carbon only discovered in 1985. Smoky form of carbon only discovered in 1985. Smoky Bunsen flames have them as well!Bunsen flames have them as well!

The reason why they were not found earlier is The reason why they were not found earlier is that few of these molecules survive the flames!that few of these molecules survive the flames!

Respiration is the oxidation of sugars in our bodies to produce energy.

respirationrespiration

when we breathe, the blood in our lungs takes in oxygen

oxygen will then react with sugars in our bodies to produce energy and carbon dioxide

sugar + oxygen carbon dioxide + water + energy

oxidation of sugars in our bodies to provide energy for

games

comes from the food we eat

will be breathed out

oxygen

http://app.mewr.gov.sg/home.asp?id=M1 Clean Card

air pollution

PollutantsPollutants Major SourcesMajor Sources Harmful Harmful EffectsEffects

Treatment or Treatment or PreventionPrevention

carbon monoxide

incomplete combustion of carbon fuels

headaches; breathing

difficulties; can kill people

supply excess air to ensure complete combustion; fit vehicles with

catalytic converters

methane

bacterial decay of vegetation; farm animals and rice

growing

global warming no easy solutions

oxides of nitrogen

lightning; vehicle engines

breathing difficulties; acid rain; produces

ozone

fit vehicles with catalytic converters

air pollutionAir around us contains pollutants, which are harmful substances to the environment

Air around us contains pollutants, which are harmful substances to the environment

air pollution

PollutantsPollutants Major SourcesMajor Sources Harmful Harmful EffectsEffects

Treatment or Treatment or PreventionPrevention

ozone

sunlight acting on unburnt

hydrocarbons and nitrogen dioxide

irritates eyes and lungs;

asthma attacks

reduce vehicle emissions of pollutants

sulfur dioxide

combustion of fossil fuels – especially coal; volcanoes’

eruptions

breathing difficulties;

asthma attacks; acid

rain

burn less sulphur-containing fuels; absorb SO2 from chimney gases with calcium carbonate

unburnt hydrocarbons

vehicle enginesproduces

ozone

fit vehicles with catalytic

converters

colourless and odourless gas

some of the CO in the air is natural, from the result of forest fires.

colourless and odourless gas

some of the CO in the air is natural, from the result of forest fires.

air pollutioncarbon monoxide (CO)carbon monoxide (CO)

comes from the incomplete combustion of fuel in vehicles; all new motor cars in Singapore are fitted with catalytic converters; oxidises CO to CO2

comes from the incomplete combustion of fuel in vehicles; all new motor cars in Singapore are fitted with catalytic converters; oxidises CO to CO2

can be absorbed by haemoglobin in the blood, thus blood can no longer absorb O2

can be absorbed by haemoglobin in the blood, thus blood can no longer absorb O2

carbon monoxide (CO)carbon monoxide (CO)

extra amounts of CO result in tiredness, headaches, heart damage and small amounts can be lethal

extra amounts of CO result in tiredness, headaches, heart damage and small amounts can be lethal

• Before absorption of CO:

O2 + haemoglobin oxyhaemoglobin

(moves through the body to release O2 when needed)

• After absorption of CO:

CO + haemoglobin carboxyhaemoglobin

(does not absorb O2)

air pollution

fuels (coal and petroleum) contain sulfur as an impurity; when fuels are burnt, sulfur is oxidised to SO2

fuels (coal and petroleum) contain sulfur as an impurity; when fuels are burnt, sulfur is oxidised to SO2

sulfur dioxide (SO2)sulfur dioxide (SO2)

is also emitted from volcanoes’ eruptions

irritates the eyes and causes breathing difficulties; main cause of acid rain

is also emitted from volcanoes’ eruptions

irritates the eyes and causes breathing difficulties; main cause of acid rain

volcanoes: natural source of

SO2 pollution

air pollution

in Singapore, there are measures to reduce the emission of SO2 into the atmosphere:

in Singapore, there are measures to reduce the emission of SO2 into the atmosphere:

sulfur dioxide (SO2)sulfur dioxide (SO2)

o oil fuels are not allowed to contain more than 2% sulfur

o exhaust gases from power stations and industries are treated with CaCO3 to remove acidic SO2

o oil fuels are not allowed to contain more than 2% sulfur

o exhaust gases from power stations and industries are treated with CaCO3 to remove acidic SO2

volcanoes: natural source of

SO2 pollution

air pollution

sulfur dioxide (SO2)sulfur dioxide (SO2)

Calcium carbonate are strongly heated and partly decomposed to give alkaline calcium oxide.

CaCO3(s) CaO(s) + CO2(g)

The exhaust gases are treated with a wet mixture of calcium carbonate and calcium oxide.

CaCO3(s) + SO2(g) CaSO3(s) + CO2(g)

CaO(s) + SO2(g) CaSO3(s)

Calcium carbonate are strongly heated and partly decomposed to give alkaline calcium oxide.

CaCO3(s) CaO(s) + CO2(g)

The exhaust gases are treated with a wet mixture of calcium carbonate and calcium oxide.

CaCO3(s) + SO2(g) CaSO3(s) + CO2(g)

CaO(s) + SO2(g) CaSO3(s)

air pollution

sulfur dioxide (SO2)sulfur dioxide (SO2)

CaCO3(s) + SO2(g) CaSO3(s) + CO2(g)

CaO(s) + SO2(g) CaSO3(s)

Calcium sulfite react with air to from calcium sulfate, and then dumped.

Limestone is used because it is cheap.

CaCO3(s) + SO2(g) CaSO3(s) + CO2(g)

CaO(s) + SO2(g) CaSO3(s)

Calcium sulfite react with air to from calcium sulfate, and then dumped.

Limestone is used because it is cheap.

air pollution

At high temperatures, nitrogen and oxygen combine to form nitrogen monoxide:

N2(g) + O2(g) 2NO(g)

The nitrogen oxide combines with more oxygen to become nitrogen dioxide:

2NO(g) + O2(g) 2NO2(g)

These two oxides of nitrogen are often describe simply as NOx.

At high temperatures, nitrogen and oxygen combine to form nitrogen monoxide:

N2(g) + O2(g) 2NO(g)

The nitrogen oxide combines with more oxygen to become nitrogen dioxide:

2NO(g) + O2(g) 2NO2(g)

These two oxides of nitrogen are often describe simply as NOx.

nitrogen oxides (NO and NO2)nitrogen oxides (NO and NO2) air pollution

oxides of nitrogen (NO and NO2) are produced naturally in lightning and forest fires

excess man-made production of oxides of nitrogen is harmful; found inside motorcar engines, power stations and industries

damage people’s lungs and react with other pollutants to form ozone

oxides of nitrogen (NO and NO2) are produced naturally in lightning and forest fires

excess man-made production of oxides of nitrogen is harmful; found inside motorcar engines, power stations and industries

damage people’s lungs and react with other pollutants to form ozone

air pollutionnitrogen oxides (NO and NO2)nitrogen oxides (NO and NO2)

preventive measure: motorcars are fitted with catalytic converters to reduce oxides of nitrogen to N2

o Not in syllabus: the redox reactions in Catalytic Converter to remove combustion pollutants.

preventive measure: motorcars are fitted with catalytic converters to reduce oxides of nitrogen to N2

o Not in syllabus: the redox reactions in Catalytic Converter to remove combustion pollutants.

air pollutionnitrogen oxides (NO and NO2)nitrogen oxides (NO and NO2)

Quick Check

Car exhaust fumes are a major source of air pollution. What pollutants are present in car exhaust?

Answer:

Carbon monoxide, sulfur dioxide, oxides of nitrogen and unburnt hydrocarbons are present in car exhaust fumes.

Carbon monoxide

Unburnt hydrocarbonssulfur dioxide

Oxides of nitrogen

Smoke and soot

Key

sulfur dioxide (SO2) and nitrogen dioxide (NO2) are acidic oxides that react with oxygen and water vapour in the air to form sulphuric acid and nitric acid which become acid rain

sulfur dioxide (SO2) and nitrogen dioxide (NO2) are acidic oxides that react with oxygen and water vapour in the air to form sulphuric acid and nitric acid which become acid rain

acid rainacid rain

SO2 + oxygen + water vapour

NO2 + oxygen + water vapour

sulphuric acid

nitric acid

acid rainatmosphereacidic oxides

air pollution

typical pH of acid rain is 4 which is 1000 times more acidic than clean water

Pure water has a pH of 7, and rainwater has a pH of 5.6.

typical pH of acid rain is 4 which is 1000 times more acidic than clean water

Pure water has a pH of 7, and rainwater has a pH of 5.6.

acid rainacid rain air pollution

acid corrodes buildings and

metal structures

soils acidified

acid kills fish

lakes acidified

acid damages trees through

roots

gases damage green leaves

sulphuric acid nitric acidACID RAIN

gases react with air and water in clouds

coal, oil, fossil fuels burned

acid rainacid rain harmful effects: harmful effects:

o corrodes the cement and stones used in buildings

o corrodes the steel structures such as fences and bridges

o kills fishes in fresh water lakeso makes agricultural land acidic thus crops grow poorly

o corrodes the cement and stones used in buildings

o corrodes the steel structures such as fences and bridges

o kills fishes in fresh water lakeso makes agricultural land acidic thus crops grow poorly

damage to left statue caused by

acid rain

air pollution

acid rainacid rain prevention: prevention:

o burn fuels that contain less sulFur(which is why oil and natural gas is preferred instead of coal for power stations)

o neutralise acidic oxides from power stations with alkalis before they are released into the atmosphere

o fit motor cars with catalytic converters to reduce the emission of nitrogen oxides

o adding calcium hydroxide to lakes and soils to neutralise the acid

o burn fuels that contain less sulFur(which is why oil and natural gas is preferred instead of coal for power stations)

o neutralise acidic oxides from power stations with alkalis before they are released into the atmosphere

o fit motor cars with catalytic converters to reduce the emission of nitrogen oxides

o adding calcium hydroxide to lakes and soils to neutralise the acid

air pollution

acid rainacid rain

NOTE:

These methods are not very effective as the damage has already been done. The only effective way to halt acid rain damage is to stop releasing acidic oxides into the air.

air pollution

42

Question 1

Which is the most common gas in air? A. Ar

B. CO2

C. O2

D. H2O

Answer: C

43

Question 2

Which pollutant causes the greatest corrosion of steel structures?A. Carbon monoxide

B. Methane

C. Ozone

D. Sulfur dioxide

Answer: D

44

Question 3

What is a natural source of sulfur dioxide pollution in the atmosphere? A. combustion of diesel fuel

B. volcanoes

C. lightning

D. incomplete combustion of methane

Answer: B

45

Question 4

Molecules present in the exhaust gases from a motorcar engine include argon, carbon dioxide, carbon monoxide, methane, nitrogen, nitrogen dioxide and water vapour. Which of these gases are also found in unpolluted air? A. nitrogen only

B. nitrogen, carbon dioxide and water vapour only

C. argon, methane, nitrogen, and water vapour only

D. argon, nitrogen, nitrogen dioxide, carbon dioxide and water vapour only

Answer: D

46

Question 5

Which pollutants can be removed from the chimney gases of factories and power stations by treatment with calcium carbonate? A. carbon monoxide and sulfur dioxide

B. nitrogen dioxide and sulfur dioxide

C. methane and ozone

D. nitrogen dioxide only

Answer: B

Acknowledgement:Acknowledgement:

• www.longman.com www.longman.com

• Marshall Cavendish International Marshall Cavendish International (Singapore) Pte. Ltd.(Singapore) Pte. Ltd.