4. FOSSIL FUEL COMBUSTION, Air Pollution
AIR POLLUTION - sources and effects
of sulfur and nitrogen oxides
Anthropogenic means any
environmental change or pollution due to human activity and there is a
lot of it about on 'Planet Earth'
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4D Fossil fuel combustion air pollution, sulfur oxides, nitrogen oxides, acid rain
and how catalytic converters remove pollutants from
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Fossil fuel air pollution
incomplete combustion, carbon monoxide & soot particulates
4B Pollution, Accidents
and Economic Aspects of the Petrochemical Industry
Greenhouse effect, global warming, climate change,
carbon footprint from fossil fuel burning
local acid rain project!!!
There were three coal-fired power stations here, the last
coal-fired Ferrybridge power station C closed in 2016.
4D AIR POLLUTION - sulfur oxides and nitrogen oxides
ACID RAIN and dealing with sulfur dioxide
OTHER POLLUTANTS including dealing with nitrogen oxides and
particulates using catalytic converters
Carbon monoxide and carbon
particulates were initially dealt with in section 4A,
but they are mentioned here again in the context of three way catalytic
combustion also produces other pollutants including ...
Nitrogen oxides collectively denoted by
NO is formed in car engines and changes to NO2,
which is acidic with water, contributing further to acid rain (above), and
are also involved in the chemistry of 'photochemical smog'
- which produces chemicals harmful to respiration, irritating to
eyes and lungs, causes headaches and tiredness and contributes to acid rain.
of the reactions are initiated by sunlight acting on the oxides of
nitrogen and other chemicals in the air.
is formed in high temperature combustion situations e.g. car
engines, power station furnace burning coal, oil or natural
gas (temperatures can be up to 1000+C in a car engine).
and in air the
nitrogen monoxide rapidly combines with the oxygen in air
dioxide is oxidised to nitric acid by the reaction with oxygen
from air when it dissolves in rainwater - contributing, with
sulfur dioxide, to making 'acid rain'.
Carbon monoxide CO,
which is toxic, and also involved in the chemistry of
'photochemical smog' (see 4A
This is formed by inefficient
incomplete combustion of hydrocarbon fuels.
There are legal limits
on emissions allowed from car exhaust systems and these are checked
every year as part of the MOT test (at least in the UK, not sure on
hydrocarbons, CxHy, which can be
carcinogenic and are also involved in photochemical smog
Some of these hydrocarbons
can pass through the engine without being oxidised.
belong to a group of chemicals known as volatile organic
In the atmosphere the VOCs
react with nitrogen oxides (e.g. NO2) in sunlight to
produce a photochemical smog haze - a very unpleasant and
converters can significantly reduced these three unwanted
CO and NO, and CxHy (x and y are at
least 6) gets
oxidised to CO2 and H2O).
platinum-rhodium transition metal catalysts, these are
dispersed on ceramic bed to give a big surface area for the
best reaction rate.
hydrocarbons + oxygen == catalyst => carbon dioxide and water
and the removal of
polluting nitrogen oxides by conversion to nitrogen ..
2CO(g) == catalyst ==> N2(g) + 2CO2(g)
The catalyst works best at high
temperature AND the catalyst is fabricated to give the largest
possible surface area to give the maximum rate of reaction -
typical rate of reaction factors controlling the speed of this
There are other indirect
pollution problems to do with burning fossil fuels:
Nitrogen dioxide (NO2) is a
lung and eye irritant, and, along with nitrogen monoxide, it is
involved in the complex chemistry of photochemical smogs which can
also produce ozone and other harmful chemicals in the air.
Lead compounds used to be
added to petrol to improve engine performance.
Photochemical smog was
mentioned in the previous paragraph.
However, ultimately, the
only way to reduce atmospheric pollution from fossil fuel burning,
is to burn less of fossil fuels and develop other sources of energy
to generate electricity and power road vehicles etc.
More on catalytic converters
(for advanced A level students)
A catalyst is a substance that
increases the speed of a reaction by providing a pathway of
lower activation energy compared to the uncatalysed reaction,
but is unchanged at the end of the reaction.
In this case catalytic converters
use metals like platinum, rhodium and palladium on the catalyst bed.
These catalyst beds are designed
to maximise the surface area over which the car exhaust gases
pass - this further increases the rate of the catalysed reactions
i.e. the improves the efficiency of pollutant removal.
The catalytic converters are
fitted into the exhaust system of a motor vehicle.
The inside of a catalytic
converter is a honeycomb of a high temperature resistant
ceramic material coated with thin layers of the metal catalyst.
The honeycomb ensures the gases
flow over a large surface area to further speed up the
A lambda probe can measure the
oxygen level in the exhaust gases.
These are called heterogeneous
catalysts because the catalyst solid) is in a different phase or
physical state than the reactants (gases).
A modern three-way catalytic
converter involves three reactions - a reduction and two
The reduction, using a platinum
rhodium catalyst, converts nitrogen monoxide to nitrogen and oxygen.
1st oxidation reaction oxidises
carbon monoxide to carbon dioxide using a platinum-palladium
2nd oxidation reaction oxidises
unburned hydrocarbons to carbon dioxide and water, uses same Pt-Pd
Catalytic converters can convert
at least 90% of the gases to less polluting and harmful gases.
The catalysts used in catalytic
converters e.g. platinum, rhodium and palladium, are very expensive
metals, but they have the advantage of not corroding easily.
Cheaper metals like nickel and
copper are also good catalysts but are easily oxidised - poisoned,
and lose their ability to catalyse the reactions.
The honeycombed structure of the
catalytic converter can also be contaminated with particles sticking
to the surface, again reducing the efficiency of the reactions.
For advanced A level chemistry
more details on heterogeneous catalysts.
A little local acid rain
For over 25 years. Tom Chadwick
and Phil Brown have been monitoring the pH of almost all the rain
that has ever fallen on the village of Castleton, set on a ridge,
500 ft up on the North York Moors in north-east England.
Equipment, method and
We use a simple water collector
to measure rainfall and a Jenway pH meter that reads to two decimal
Jenway is a good brand, but
not cheap! Check out eBay! Jenway 370 pH meter
The pH meter is calibrated with pH 4
and pH 7 buffers, which cover the range of most pH values we
The samples are stored for a
few days and tested in batches each week.
You need to keep a check on
the calibration of the pH meter and probe and instructions are
supplied on how to calibrate and store the equipment.
Measuring the rainfall is an
optional extra - the more data the better!
Comments on results so far
Generally speaking, there has been
a steady decline in 'acid rain incidents' and the average pH has
For electricity production, this would be expected as
fossil fuel power stations are coming to the end of their
working lives in the UK and coal is being replaced by natural
gas, renewable energy - particularly wind turbines.
The figures for the UK in 2017
are: Natural gas 40%, coal 7%,
renewables (wind, solar, hydroelectric) 30%, nuclear 21% and 2% from
other sources. This is part of a good trend as we become less
reliable on fossil fuels in the UK.
BUT, lately, as listed below,
some quite acid rain has been falling on the North York Moors!
Therefore, as regards Europe
(including the UK) acid rain is still an environmental pollution
1. Wouldn't this make a
good, and not too complicated, environment science project for
All you need is:
a rainwater collector
- with a wide funnel for low rainfall,
VERY clean plastic
sample bottles to temporarily store the samples (do a
batch every week),
a 'quality' pH meter
and probe - preferably calibrated with pH 4 and pH 7
and somebody to check
the wind direction from a TV/internet weather chart.
Schools could x-check
their results with other schools and us.
2. Natural unpolluted
rainwater has a pH of 5.65, slightly acidic due to the
dissolving of the weakly acid gas carbon dioxide. 'Carbonic
acid' ('H2CO3') is considered to be formed
which ionises to a very small degree to give the acidic hydrogen
H+(aq) + HCO3-(aq)
The equilibrium position
is very much on the left-hand side and the weakly acidic
equilibrium pH of 5.65 is the result of the current carbon
dioxide level of just over 400 ppm. The pH is temperature
Increasing carbon dioxide
levels in the atmosphere will slightly increase the acidity
of seas and oceans and this will have ecological
Advanced A level
The pH of a solution
is defined a minus the logarithm to the base 10 of the
hydrogen ion (H+) concentration in moles/dm3.
pH = -log10[H+(aq)],
which translates as [H+(aq)]
The pH is
slightly dependent on temperature.
Since the pH scale is
based on logarithm base 10, each pH unit represents a
factor of x 10 in the concentration of hydrogen ions.
implications for how you view the relative acidity
of your water sample.
The background pH
on unpolluted water is ~pH 5.6.
If an 'acid
rain event' happens and the pH of the rain water
is as low as pH 3.6, it means the rain is 10 x 10 =
100 times more acidic than unpolluted rain!
3. The optimum pH for most
fish life and other aquatic creatures is 6.5 to 9.0.
Salmon prefer a water of
pH 7.0 to 8.0. Acid rain falling into, and accumulating in
lakes and rivers can have a devastating effect on fish
Fish can adjust to pH
values down 6 as long as there is no sudden change or
fluctuation in the level of acidity.
Aquatic life becomes
seriously affected if the pH of the water falls below pH 5.
Fish begin to die if
the water pH falls below pH 4.
4. Acid rain has, still does,
cause destruction to forests and corrosion of stone buildings.
Some recent 'acid rain
events' recorded - most rain these days has a pH of 5 to 7
||Possible air mass from Eastern Europe? - coincidentally,
on the BBC news was an item on the large quantities of coal
being burned in Poland and other Eastern European countries
- its an unfortunate important aspect of their economies!
||Possibly from UK fossil fuel plants
in south of Castleton e.g. in Yorkshire and the Midlands?
||'acid rain' origin southern-midlands UK?
||'acid rain' origin Continent?
||'acid rain' origin southern-midlands UK?
||'acid rain' origin Continent?
||origin of acid rain?
||fossil fuelled power stations
midlands of England?
||No acid rain events worth recording - a good sign in the
||Location: Castleton village, North Yorkshire
Sometimes from the E/SE we get polluted air
mass from continental Europe - fossil fuel east European
Not sure on the acid rain from the SW, now there are very
few fossil fuels power stations in the UK.
The is a biomass power station 60 miles SSW of the
There are three active fossil fuel power stations
in the UK
West Burton, Nottinghamshire, England, south of
Ratcliffe on Soar, Nottinghamshire, England,
south of my location
Kilroof, County Antrim, NI, quite
some distance west of my location
All three to close by
the end of 2024
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air pollution from sulfur oxides and nitrogen oxides Urban Outfitters,
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