Environmental chemistry
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study of the effect of human
activity on the chemical processes in
the environment
concerns political and natural borders
global issues
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
Environmental chemistry
E1: air pollution
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Describe the main sources of carbon
monoxide (CO), oxides of nitrogen (NOx),
oxides of sulfur (SOx), particulates and
volatile organic compounds (VOCs) in the
atmosphere.
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Evaluate current methods for the reduction of
air pollution.
the
atmosphere
composition of dry clean air
http://www.dep.state.pa.us/earthdaycentral/97/air_teachers/TAB1.htm
component
content
component
% by Vol.
ppm
Nitrogen
78.09
780,900
Oxygen
20.94
Argon
content
% by Vol.
ppm
Hydrogen
.00005
0.5
209,400
Methane
.00015
1.5
.93
9,300
Nitrogen
dioxide
.0000001
0.001
Carbon dioxide
.0318
318
Ozone
.000002
0.02
Neon
.0018
18
Sulfur dioxide
.00000002
0.0002
Helium
.00052
5.2
Carbon
monoxide
.00001
0.1
Krypton
.0001
1
Ammonia
.000001
0.01
Xeon
.000008
0.08
Nitrous oxide
.000025
Units used to express amount of a gas
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% by volume
ppm = parts per million/particles per million
particles
Remember in gases, assuming conditions are
the same:
same volume = same number of particles
So 78.09 % by volume is 78.09 % particles
per million particles or 780,900 ppm
primary air pollutants
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waste products from human activity
primary = added directly to the air
pollutant = chemical in the wrong
concentration in the wrong place
primary air pollutants:
CO
NOx
particulates
SOx
volatile organic compounds (VOCs)
Air pollutants
For each air pollutant you need to know:
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sources: natural and man-made
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 + ½ O2  CO + 2H2
natural forest fires
Man-made:
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incomplete combustion of carbon-containing
fuels; mainly in cities; localized problem as well as fluctuations
during the day – heavy traffic.
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forest fires
carbon monoxide: health effect
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CO combines with Fe in haemoglobin in blood –
bonds 320 times stronger than oxygen – oxygen
cannot bond onto heamoglobin.
Less oxygen supplied to body cells.
Effects:
 headaches,
 shortness of breath,
 in case of high concentration (e.g. rush hour):
unconsciousness, death.
carbon monoxide: reduction (1)
Lean burn engines
Decrease fuel /air
ratio (in mass) from
1:14.7 (stoichiometric
ratio/green band in
diagram) to 1:18.
Why?
(or increase air /fuel
ratio to 18:1)
carbon monoxide: reduction (2)
catalytic converter in car exhaust system
 reduction of nitrogen oxide
 oxidation of CO and unburnt
hydrocarbons/VOCs
2CO (g) + O2 (g) 
2CO2 (g)
2NO (g) + 2CO (g) 
2CO2 (g) + N2 (g)
2C8H18 (g) + 25O2 (g)  16CO2 (g) + 18H2O (g)
Catalytic converter
catalytic converter
To achieve high rate of reaction for this
redox process:
 exhaust gases are passed over platinum
which acts as a heterogeneous catalyst;
 converter has a honey comb structure to
increase surface area;
 very high temperature of the exhaust gases
also increase the rate of reaction
dramatically.
Thermal exhaust reactor
Heat from engine makes CO react with
more air to oxidise it further to carbon
dioxide.
sulphur oxides: sources
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Natural:
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volcanoes
sea spray
biological decay of organic matter that
contains sulphur
reduction of sulphates
Man-made:
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coal-burning power stations (equation
starting from S in coal)
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roasting of metal sulphides e.g. ZnS and
Cu2S (equation)
sulphur oxides: health effects
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acidic oxides
lung irritants, affect in particular those
suffering from respiratory problems e.g.
asthma sufferers
formation of sulphuric acid aerosols (droplets
of sulphuric acid) (equation) (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
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use of “low-sulphur content” fuels or removal
of sulphur before burning coal/oil
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removal of SO2 from fumes before they are
released:
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limestone based fluidised bed (equations showing
decomposition of calcium CaCO3 reaction of CaO with SO2)
alkaline scrubbing (wet scrubber) (equations showing
reaction of CaO and Mg(OH)2)
Sulphur oxides: reduction (1)
Wet
scrubber
Limestone based fluidised bed
nitrogen oxides: sources
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Natural:
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Electrical storms release enough energy to cause
oxidation of atmospheric nitrogen: (equations showing
oxidation of nitrogen and further oxidation of NO)
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Decomposition of organic matter containing
nitrogen
Man-made: Combustion of fossil fuels in car engines
and furnaces of power stations produces high
temperatures to cause oxidation : (equation showing oxidation
of nitrogen)
nitrogen oxides: health effects
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choking irritating gas, affects eyes and people
with respiratory problems
forms nitric acid aerosols/acid rain (equation showing
dissolution of nitric acid in water)
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nitric acid also increases the rate of oxidation of
SO2 (see later)
plays an important role in the formation of
secondary pollutants e.g. ozone and smog
nitrogen oxides: reduction
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catalytic converter
lean burn engines: high air/fuel ratio or low
fuel/air
recirculation/reburn of exhaust gases: 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.
Particulates: sources
particulates = airborne/suspended liquid and solid
particles.
 Natural:
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volcanic eruptions
large forest fires
Man-made:
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burning fossil fuels e.g. diesel
forest fires
industrial emissions; chemical processes
incinerators
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
Electrostatic precipitator
.
Particulates are given a
negative charge and
then attracted onto
positively collection
plates
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
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