Environmental chemistry
air pollution
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Option E in Paper 3
study of the effect of human activity on
the chemical processes in the
environment
concerns political and natural borders
global issue
applied chemistry
Main topics: core
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air pollution
acid deposition
greenhouse
effect
ozone depletion
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dissolved
oxygen in water
water treatment
soil
waste
Main topics: AHL
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ozone depletion
smog
acid deposition
water and soil
Where is the air?
What is air?
Gas
N2
O2
Ar
Water vapour
CO2
%
78
21
1
0-4
0.04
How does the
temperature
change in the
atmosphere?
Primary air pollutants
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Substance that has harmful effect on
environment
waste products from human activity
added directly to the air
pollutant = chemical in the wrong concentration
in the wrong place
primary air pollutants:
CO
SOx
NOx
particulates
volatile organic compounds (VOCs)
Secondary – primary pollutants undergo chemical changes in the
atmosphere
Air pollutants
For each air pollutant you need to know:
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sources: natural and man-made
(effects on health)
methods of reducing its emissions
any relevant balanced symbol equations
Carbon monoxide: sources
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Natural:
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atmospheric oxidation of methane
CH4 + 1/2O2  CO + 2H2
natural forest fires
Man-made: (anthropogenic)
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incomplete combustion of carbon-containing
fuels (fossil fuels); mainly in cities: localized problem as well as
fluctuations during the day – rush hour
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2C(s) + O2(g)  2CO(g)
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forest fires
Carbon monoxide: health effect
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CO combines with Fe in hemoglobin in blood
more effectively than oxygen – therefore oxygen
cannot bond onto hemoglobin
Less oxygen supplied to body cells
Effects:
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headaches, dizziness
shortness of breath,
in case of high concentration : unconsciousness, death
Colorless and odorless so very dangerous
Carbon monoxide: reduction (1)
Lean burn engines: have
controlled fuel injections
which keep air/fuel ratio of
18 and produce low CO
emissions.
Fuel ratios of 12.5 are usually produced for max
power b/c it is rich in fuel and low in air.
Need this fuel for engine to work properly.
This increases the CO levels produced.
Combustion of octane:
2C8H18 (g) + 25O2 (g) 
16CO2 (g) + 18H2O
Carbon monoxide: reduction (2)
Catalytic converter - hot gases mix with air and are passed
over a platinum catalyst.
Two Types of Catalyst:
1. Oxidation catalyst – used in lean burn engines to convert CO to CO2.
2CO (g) + O2 (g)  2CO2 (g)
2. Three way catalyst – used in conventional engines to oxidize CO to
CO2 and hydrocarbons to water. They also reduce NO to N2.
2NO (g) + 2CO (g)  2CO2 (g) + N2 (g)
Results in 90% reduction of pollution without loss of engine
performance.
Catalytic converter
Carbon monoxide: reduction
Thermal Converters
Thermal Exhaust reactor – takes advantage of the heat of the exhaust
gases and makes the CO react with more air to produce CO2. Any
unburned volatile organic compounds such as hydrocarbon fuels are
also oxidized to CO2 and H2O.
2CO (g) + O2 (g)  2CO2 (g)
CxHy + O2  xCO2 + y/2 H2O
Sulphur oxides: sources
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Natural:
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volcanoes (SO2)
sea spray
biological decay of organic matter
which contains sulphur (veggies)
reduction of sulphates
Oxidation of hydrogen sulfide
2H2S + 3O2  2SO2 + 2H2O
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Man-made:
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coal-burning power stations
S(s) + O2  SO2
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Smelting plants
Cu2S(s) + 2O2  2CuO + SO2
Sulphur oxides: sources
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Sulfur trioxide –
Secondary pollutant formed in the
atmosphere between the primary pollutant
SO2 and O2. SO3 can dissolve in water to
form sulfuric acid.
2SO2 (g) + O2(g)  2SO3(g)
H2O(l) + SO3(g)  H2SO4(aq)
Overall:
2H2O(l) + 2SO2(g) + O2  2H2SO4(aq)
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Sulphur oxides: health effects
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acidic oxides
lung irritants, affect in particular those suffering
from respiratory problems e.g. asthma
formation of sulphuric acid aerosols (droplets of
sulphuric acid) (often catalysed by metal particulates);
effects of aerosols:
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irritant to the eyes
irritate vessels in lungs causing impaired breathing
Sulphur oxides: methods of reduction
S can be removed before or after combustion
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removal of SO2 from fumes before they are
released:
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Sulfur in coal can be removed by crushing it
and washing with water.
Impurities in crude oil can be removed by
mixing with KCO3 (basic):
H2S + CO3-  HS- + HCO3-
Sulphur oxides: methods of reduction
S can be removed before or after combustion
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removal of SO2 from fumes after they are
released:
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alkaline scrubbing:(wet scrubber) (also called
flue gas desulphurization): an alkaline
mixture is sprayed downwards into the
exhaust gases.
Sulphur oxides: reduction
Wet
scrubber
Sulphur oxides: methods of reduction
S can be removed before or after combustion
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Alkaline Scrubbing: 2 types
Mixture includes: CaO (lime) or CaCO3 (limestone)
CaO + SO2  CaCO3 (s)
CaCO3(s) + SO2  CaSO3(s) + CO2
2CaSO3 + O2  2CaSO4(s)
CaSO4 can be deposited in landfill or used to make plasterboard.
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Mixture includes: MgO
MgO (s) + SO2(g)  MgSO3 (s)
MgO can be regenerated from the product (decomposition)
SO2 is used in the manufacturing of sulfuric acid.
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Sulphur oxides: methods of reduction
S can be removed before or after combustion
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removal of SO2 from fumes after they are
released:
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Fluidized combustion: coal is mixed with
powdered limestone on a metal plate. A
strong air flow passes through the mixture
from below and makes the particles of
limestone and coal float above the plate
making the mixture behave like a fluid.
Sulphur oxides: methods of reduction
S can be removed before or after combustion
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Fluidized combustion:
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Heat produced from the combustion of coal causes CaCO3 to
break up into CaO(s) and CO2
Sulfur dioxide is removed as it is formed in the combustion of
coal. CaO reacts with SO2:
CaO + SO2  CaSO3
2CaO + SO2 + O2  2 CaSO4 (s)
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Sulphur oxides: reduction
Limestone
based
fluidized
bed
Nitrogen oxides: sources
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NO, NO2, and N2O (causes photochemical smog and forms HNO3 (acid
rain))
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Natural:
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Electrical storms release enough energy to cause oxidation of atmospheric
nitrogen: N2 + O2  2NO (lightening)
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Decomposition of organic matter containing nitrogen produces N2O
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Man-made:
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40% cars: N2 + O2  2NO (under high temp)
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30% coal and oil power stations
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20% burning fossil fuels
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10% other
Photochemical smog is brown due to presence of NO2
2NO + O2  2NO2
Nitrogen oxides: health effects
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choking irritating gas, affects eyes and
people with respiratory problems
forms nitric acid aerosols/acid rain
nitric acid also increases the rate of
oxidation of SO2
plays an important role in the formation of
secondary pollutants e.g. ozone and smog
Nitrogen oxides: reduction
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Three-way catalytic converter:
2CO + 2NO  2CO2 + N2
lean burn engines: high air/fuel ratio or low fuel/air
Recirculation of exhaust gases (EGR): nitrogen oxide emissions are
reduced by reintroducing exhaust gases into the fuel mixture, lowering
peak combustion temperatures as it is the high temperature in the
combustion engine which causes nitrogen oxide production. Reduces
NO emissions.
Particulates: sources
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particulates = airborne/suspended liquid and solid particles (particles
of C or dust) (particulates are polar and attract to water molecules and
form aerosols)
Natural:
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Sulfur from volcanic eruptions
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large forest fires
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Pollen, bacterial, and fungal spores
Man-made:
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burning fossil fuels e.g. diesel
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forest fires
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industrial emissions; chemical processes
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Incinerators
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Arsenic from insecticides
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Asbestos used in construction
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Mercury from manufacturing of fungicides and paper
Particulates: health effects
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particulates penetrate lungs and may block
air passages
some are poisonous e.g. Pb and asbestos
adsorb chemicals and can act as catalysts in
reactions producing secondary pollutants
by adsorbing also increase concentration
and rate of reaction
reduce visibility
Particulates: reduction
Particulates and aerosols are removed
naturally by rain and snow
(gravitational settling)
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Ways to prevent them from entering
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the atmosphere include:
Filtration, centrifugal separation, settling
tanks, scrubbing, and electrostatic
precipitation
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Electrostatic precipitator: particulates
are charged negatively and then
attracted onto positively collection
plates
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Settling tanks: “dirty” air enters a
chamber and dust will settle out by
gravity
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Particulates: reduction
Volatile organic compounds: sources
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Natural sources:
 methane: bacterial anaerobic decomposition of
organic matter (e.g. in rice paddies)
 from plants e.g. terpenes
 leakage from natural fossil reserves
Man-made:
 evaporation of fuels
 partial combustion of fuels
 leakage from storage reservoirs
 Solvents and paints
VOCs: health effects
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photochemical smog
can lead to carcinogenic compounds
fatigue, weakness
respiratory problems
VOCs: reduction
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catalytic converter
Thermal exhaust reactor
Summary