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Air pollutants from natural sources
~Volcano produces sulphur dioxide
~ Biological processes
e.g. Digestion in cows
produces large amounts of
methane.
Methane is an air pollutant
Air pollutants from human
activities
* cars burn petrol or diesel
* power stations burn coal
* factories burn heavy oil
Atmospheric
pollutants
1. Carbon monoxide and carbon
2. Unburnt hydrocarbons
3. Sulphur dioxide
4. Oxides of nitrogen
5. Photochemical smog
6. Lead compounds and Heavy Metals
7. Particulates
8. Ozone
9. Benzene
10. 1,3-butadiene
11. TOMPs (Toxic Organic Micropollutants)
1. Carbon monoxide and carbon
• Carbon monoxide (CO) is a toxic gas
• emitted into the atmosphere by
incomplete combustion processes
• formed by the oxidation of hydrocarbons
and other organic compounds.
• survives in the atmosphere for a period
of approximately 1 month
• is eventually oxidized to carbon dioxide
(CO2).
• Carbon particles are part of the dark
smoke that forms.
• In urban areas, CO is produced almost
entirely (90%) from road traffic
emissions.
• CO at levels found in ambient air may
reduce the oxygen-carrying capacity of
the blood.
• Low conc.: dizzy, headache and
irritable
• High conc.: unconsciousness and death
2.Unburnt hydrocarbons
Two main groups of hydrocarbons :
volatile organic compounds (VOCs)
polycyclic aromatic hydrocarbons (PAHs).
VOCs :  released in vehicle exhaust gases
 emitted by the evaporation
of solvents and motor fuels.
Effect: `cause cancer
`formation of smog (smoke + fog)
3. Sulphur dioxide
Sulphur dioxide is a corrosive acid
gas.
Source : power stations burning
fossil fuels which contain
sulphur
Effect
• combines with water vapour in the atmosphere to
produce acid rain.
SO2(g)+H2O(l)
H2SO3(aq) Sulphurous acid
• damage and destruction of vegetation and in the
degradation of soils, building materials and
watercourses
• SO2 in ambient air is associated with asthma and
chronic bronchitis
• SO2 emissions effect air quality in both rural and
urban areas
• Low conc. : respiratory tracts and lung diseases
• High conc. : cancer and death
4.oxides of nitrogen
Nitrogen oxides
~formed during high temperature combustion processes from
the oxidation of nitrogen in the air or fuel.
sources: power stations, heating plants and industrial processes.
The principal source of nitrogen oxides :
- nitric oxide (NO)
- nitrogen dioxide (NO2)
Nitrogen oxides
~ mainly in the form of NO in
the atmosphere
N2(g)+O2(g)  2NO(g)
~ then oxidized to NO2 by
reaction with ozone
2NO(g)+O2(g)  2NO2(g)
Effect
• Irritation of respiratory tracts and lungs
• Exacerbate asthma
• Increase susceptibility to infections
• In the presence of sunlight ,
it reacts with hydrocarbons to produce
photochemical pollutants such as ozone.
•Nitrogen oxides have a lifetime of approximately 1
day with respect to conversion to nitric acid.
• Nitric acid is in turn removed from the atmosphere
by direct deposition to the ground, or transfer to
aqueous droplets (e.g. cloud or rainwater), thereby
contributing to acid deposition.
5. Photochemical smog
Sunlight acts on air pollutants
( e.g. carbon monoxide, nitrogen
oxides, hydrocarbons)
* form a new substance called
Photochemical smog
Effect
• Irritate the eyes
• dangerous to people with breathing and
heart problems
• poisonous to plants
• damages rubber, paint and other materials
6. Lead compounds and Heavy Metals
Particulate metals in air come from:
• fossil fuel combustion
• metal processing industries
• waste incineration
Lead ~ is the most widely used non-ferrous metal
~ use world-wide is in the manufacture of
batteries (60-70% of total consumption of
some 4 million tonnes)
~ used in paints, glazes, alloys, radiation
shielding, tank lining and piping.
Tetraethyl lead
•used as an additive in petrol to increase the
octane number
• most airborne emissions of lead from
petrol-engined motor vehicles.
Effect
• Lead is a cumulative poison to the Central Nervous
System, particularly detrimental to the mental
development of children.
• Harmful effects on red blood cells, kidney, bones,
brain
• Heart attacks, stroke, hypertension and nervous
disorder
7.Particulates
PM10 particles
~the fraction of particulate in air of very
small size <10
~ removed relatively efficiently from the air
by sedimentation.
~ primary ( emitted directly into the
atmosphere)
~ secondary (formed or modified in the
atmosphere from condensation and growth).
The atmospheric lifetime of particulate matter
~as long as 10 days for particles of about 1mm in diameter
• creating dirt, odour and visibility problems
•health effects :risk of heart and lung disease
•carry surface-absorbed carcinogenic compounds into
the lungs
•smaller particle fraction PM2.5 capable of penetrating
deepest into the lungs
8. Ozone (O3)
~a secondary pollutant
produced by reaction between
nitrogen dioxide (NO2),
hydrocarbons and sunlight
~is photodissociated itself
(split up by sunlight) to form
free radicals
~ promotes the oxidation
chemistry
~catalyses its own formation
(i.e.. it is an autocatalyst)
~ powerful oxidizing agent
Effect
• persist for several days and be transported over
long distances.
• irritate the eyes
• air passages causing breathing difficulties
• increase susceptibility to infection
• is a highly reactive chemical, capable of attacking
surfaces, fabrics and rubber materials
• toxic to some crops, vegetation and trees.
9. Benzene
Benzene ~ is an aromatic VOC.
~ is a minor constituent of petrol
( about 2% by volume)
Main sources :
refining, distribution and combustion of
petrol
Effect : human carcinogenic
10. 1,3-butadiene
1,3-butadiene ~ is a VOC emitted into the
atmosphere from fuel
combustion of petrol and diesel
vehicles.
~ is produced by the combustion of
olefins.
~ is an important chemical in
certain industrial processes,
Effect:
particularly the manufacture of
potent, human
synthetic rubber
carcinogenic
.
11. TOMPs (Toxic Organic Micropollutants)
~ produced by the incomplete combustion of fuels
~ comprise a complex range of chemicals
Compounds in this category include:
PAHs (PolyAromatic Hydrocarbons)
PCBs (PolyChlorinated Biphenyls)
Dioxins
Furans
Effect: carcinogenic.
• Ozone depletion
• The greenhouse effect
• Acid rain
The "ozone layer" is a region of relatively
high ozone concentration (at about 25 km
altitude) in the stratosphere, which is a
layer of the atmosphere between 15 and
50 km
1.Chlorofluorocarbons (CFCs)
• stable, nonflammable, low in toxicity, inexpensive to produce
•uses as refrigerants, solvents, foam blowing agents,etc.
2.Chlorine-containing compounds
e.g. methyl chloroform(solvent)
carbon tetrachloride( an industrial chemical)
3.Halons
•effective fire extinguishing agents
4.Methyl bromide
•effective produce and soil fumigant
All of these compounds
•have long atmospheric lifetimes transported by winds into the
stratosphere
• release chlorine or bromine when break down
»» strong UV radiation breaks down CFC
»» CFC molecule releases atomic chlorine
»» one chlorine atom can destroy over 100,000 ozone molecules
Example of ozone depletion ~ the annual ozone "hole" over Antarctica
ozone levels   levels of UVB reaching the Earth's surface 
Effect:
• UVB causes nonmelanoma skin cancer and plays a major role in
malignant melanoma development.
•UVB harms some crops, plastics and other materials, and certain types
of marine life.
Formation and destruction of ozone
•Sunlight - major energy source for both making and destroying
stratospheric ozone
• Up to 98% of the sun's high-energy ultraviolet light(UV-B and UV-C)
are absorbed by the destruction and formation of atmospheric ozone
Halogen catalysis of ozone
degredation
Halogens ~ a chemical family containing
fluorine, chlorine, bromine and iodine
~ catalyze ozone breakdown
Halocarbon ~ carbon compound containing
halogens
NO, NO2 and OH radicles
~ catalysts in ozone degredation in the troposphere and
lower stratosphere
The greenhouse effect
Cause
•Excessive production of CO2
Reason
•Burning a great amount of fossil fuel
forests are cleared in a great rate
Process
•Energy from the sun falls on the earth and
warms it up
the earth radiates some of the heat energy back
to the space
•CO2 absorbs some of the heat energy and
prevents it escaping from the earth atmosphere
the temperature of earth increase
Effect
• Tones of polar ice melts and flow into the
oceans. The level of the oceans would rise.
• Low-lying areas of land would be flooded
• cause severe drought in some countries
Methods to reduce the greenhouse effect
•
•
•
•
Stop cutting down forests
start new plantation
stop to use or use less fossil fuel
use alternative energy source such as solar
energy
Acid deposition
Cause :
emissions of sulphur dioxide and nitrogen oxides
Source:
•use of coal in the production of electricity
•base-metal smelting
•fuel combustion in vehicles
Formation of Acids in the Atmosphere
Converting NOx and SO2 to Acids
SO2:
Gas Phase
SO2(g)+H2O(l)  H2SO3(aq) sulphurous acid
2SO2(g)+O2(g)+2H2O(l)  2H2SO4(aq) sulphuric acid
Aqueous Phase
[S(IV)]  [SO2(aq)] + [HSO3-] + [SO3 2-]
This dissociation occurs by a two-fold process:
1) SO2 (aq)  H+ + HSO32) HSO3- (aq)  H+ + SO3 2-
NOx:
Gas Phase
2NO2(g)+H2O(l)  HNO2(aq)+HNO3(aq) nitrous acid
and nitric acid
Aqueous Phase
1. 2NO2(g) + H2O(l)  2H+ + NO3- + NO22. NO(g) + NO2(g) + H2O(l)  2H+ + 2NO23. 3NO2(g) + H2O(l)  2H+ + 2NO3- + NO(g)
ACID RAIN - A DEFINITION
pH of rainwater < 5.5
pH of normal rainwater = 5.5 to 5.7
EFFECT ON ARCHITECTURE
- damage to limestone or marble
CaCO+2H+  H2O +CO2
EFFECT ON TREES AND SOILS
- damage the plants, change the pH
of soil
EFFECT ON METALWORK
- increase the corrosion rate of
metals
EFFECT ON LAKES AND AQUATIC
ECOSYSTEMS
pH LEVEL
<6
*Basic forms of food die off.
e.g. Mayflies and stoneflies are
important food sources for fish.
They can't survive.
<5.5
*Fish cannot reproduce.
*Young have difficulty staying alive.
*More deformed adult fish due to lack
of nutrients
*Fish die of suffocation
<5.0
*Fish population die off.
<4.0
*Very different lifeforms
Reducing SO2 Emissions
Before Combustion
1. Coal Cleaning removing pyritic sulfur (FeS2)
2. Burning of Low Sulfur Coals (Subbituminous coal
is of lower sulfur content than bituminous coal.)
During Combustion
1. FBC - Fluidized Bed Combustion
After Combustion
1. Wet Flue Gas Desulfurization - The wet
scrubber consists of either limestone, lime, or
sodium hydroxide.
CaCO3 + SO2 + H2O + O2  CaSO3 + CaSO4 + CO2 + H2O
2. Dry Scrubbing - The process of dry scrubbing
involves the contact between drying gas and the
atomized liquid (alkaline based)
Reducing NOx Emissions
During Combustion
- Overfire Air
After Combustion
The catalytic reduction system - involves the injection of
ammonia gas upstream of the catalytic reaction chamber
4NO + 4NH3 + O2  4N2 + 6H2O
2NO2 + 4NH3 + O2  3N2 + 6H2O
nitrogen gas is harmless
Automobiles
Eutrophication and algal blooms
Phosphorus is the nutrient controlling the size
of freshwater blue-green algal blooms
Amount of bio-available phosphorus
(orthophosphate) 
algal blooms
A sewage treatment plant discharge
An irrigation return drain in the lower reaches, and an
upland tributary, draining a semi-agricultural catchment
Eutrophication
Diagram of the interactions (sedimentation / resuspension, uptake / release) between different
components of the aquatic environment and
orthophosphate.
• loss of fish and shellfish
EFFECT
•Human health - eating clams, mussels, oysters or scallops contaminated
by red tide can cause severe illness and even death to humans.
•Aerosols from red tides can produce respiratory ailments
•long-term consequences of inhaling potent neurotoxins from algae
• release harmful toxins causing mass mortalities of various marine
organisms
Organic pollution
Human sewage, refuse, agricultural waste like manure of
chicken and pigs and certain industrial wastes which contain
large amount of organic matter
1. Self-purification of water:
The water is well aerated when the amount of organic pollutants is
small. They are rapidly decomposed by bacteria and fungi into simple
inorganic compound.
If the amount of organic pollutants is very heavy , it will remove all
the dissolved oxygen and self -purification of water. In the absence of
oxygen the incomplete decomposition of organic matter by anaerobic
bacteria produces many unpleasant smelling gases such as methane,
ammonia and hydrogen sulphides.
Red tides are caused by the explosive population
growth of a minute, single-celled group of algae called
dinoflagellates.
1999 Hong Kong Red Tide (Unidentified species)
Oil
Millions tones of oil leak out from oil tankers.
Affects:
- oil floats on water. The oil layer prevent oxygen
dissolving in the water .
- birds lose warmth quickly when there are covered
with oil
Soapy detergents(Soap)
- an anionic surfactant
- sodium salt or potassium salt of long chain alkanoic acids
- COO- group
- from animal fats and vegetable oils
Soapless detergents(synthetic detergents/detergents)
- sodium salt salt of organic acids with a very long hydrocarbon chain
- SO3- or SO4- group
Common soap (hard soap) e.g. sodium stearate
CH3-(CH2)16-COO- Na+
Soft soap &liquid soap e.g. potassium stearate
CH3-(CH2)16-COO- K+
sodium lauryl sulphate in shampoo (soapless detergent)
CH3-(CH2) 11-O-SO3-Na+
sodium lauryl benzenesulphonate(an alkylbenzenesulphonate)
(soapless detergent) in washing powder & liquid detergent
CH3-(CH2) 11 -C6H4- SO3-Na+
AFFECT OF SOAP
1.Forms insoluble scum with
Ca 2+ &Mg 2+ of hard water
2CH3(CH2)16COO-(ag)
(CH3(CH2)16COO-)2Ca2+(s)
2.forms insoluble long chain
alkanoic acid
2CH3(CH2)16COO-(ag) 
CH3(CH2)16COOH(s)
Affect of soapless detergent
•Health problems- cause skin
allergies e.g.pH > 9 or < 5
•Branched hydrophobic chain are
non-biodegradable
•Ecological disturbance
-formation of foams in rivers
-prevent the breathing of aquatic lives
kills aquatic lives
•Phosphate additives(water softener)
speed up the growth of algae
Chemical pollution
Pesticides - poisonous chemicals deliberately sprayed
to kill a particular organism (e.g. herbicides,
fungicides and insecticides)
Thermal pollution
High temperature
- will raise the metabolic rate and oxygen consumption
of aquatic organisms
- decrease the oxygen solubility in water and the
resulting deoxygenation may seriously affect the
aquatic organisms.