FOSSIL FUEL COMBUSTION, Pollution & Climate
Brown's GCSE/IGCSE/O Level KS4 science-CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
4. Burning fossil fuels - pollution, carbon monoxide, nitrogen oxides, what makes a good fuel?,
climate change and global warming
fossil fuels like coal, oil and natural gas are extremely useful important
sources of energy, the environment does pay a price, so it is important to
understand the sources and chemistry of pollution and how its effects can be
minimised. Pollutants from fossil fuel (coal, oil, gas etc.) burning in power stations and automobile
transport include carbon monoxide, sulfur oxides and nitrogen oxides and these
in turn through photochemical reactions can produce ozone and other harmful
irritant gases. Methods of reducing pollution are described ranging from
catalytic converters in cars to desulfurising oil based fuels and flue gases.
These notes on hydrocarbon fossil fuel combustion, and pollution & climate
change issues are designed to meet the highest standards of knowledge and
understanding required for students/pupils doing GCSE chemistry, IGCSE
Level chemistry and KS4 science courses.
Index of KS4 Science GCSE/IGCSE/O Level
Chemistry Oil & Organic Chemistry revision notes pages: 1.
Fossil Fuels & carbon Cycle : 2.
Fractional distillation of crude oil & physical
properties and uses of fractions,
what makes a good fuel? : 3.
ALKANES - saturated hydrocarbons, structure, uses, combustion : 4.
Pollution, carbon monoxide, sulfur/nitrogen oxides, climate change-global warming :
5. Alkenes - unsaturated hydrocarbons,
structure and chemistry :
6. Cracking - a problem of supply and demand, other products :
7. Polymers, plastics, uses and problems :
8. Introduction to Organic Chemistry - Why so many series of
organic compounds? : 9a. Alcohols,
Ethanol, manufacture, physical properties & chemical reactions
Biofuels & alternative fuels,
hydrogen, biogas, biodiesel
: 10a. Carboxylic
acids - chemistry and uses
: 10b. Esters, chemistry and uses including perfumes
: 11. Condensation polymers, Nylon & Terylene,
comparing thermoplastics, fibres and thermosets
12. Natural Molecules - carbohydrates - sugars
- starch : 13. Amino acids, proteins,
enzymes & chromatography : 14. Oils, fats,
margarine and soaps :
15. Vitamins, drugs-analgesic medicines & food
additives and aspects of cooking chemistry! : 16. Ozone
destruction, CFC's and free
radicals : 17. Extra notes, ideas and links on
Global Warming and Climate Change : Multiple Choice and Gap-Fill Quizzes:
m/c QUIZ on Oil Products (GCSE/IGCSE easier-foundation-level)
m/c QUIZ on Oil Products (GCSE/IGCSE harder-higher-level) :
IGCSE/GCSE m/c QUIZ on other Aspects of Organic Chemistry
3 Easy linked GCSE/IGCSE Oil Products word-fill worksheets
ALL my Advanced
Level Organic Chemistry revision notes
4a. Atmospheric pollution: The Incomplete
Combustion of hydrocarbons
Introduction via coal combustion, then
onto burning hydrocarbons and pollution
The fuel coal
consists mainly of carbon, which, if burned/ignited in excess air,
combusts to form carbon dioxide.
If not enough
air/oxygen is available, coal will only 'half' burn to form the deadly
odourless, colourless and toxic gas carbon monoxide.
+ O2(g) ==> 2CO(g)
This can happen
if organic material, coal or peat is smouldering underground and is
obviously a dangerous situation.
If it was formed
in a domestic coal fire it will quite happily burn with a pale blue
flame to form the 'safe' combustion product carbon dioxide gas.
+ O2(g) ==> 2CO2(g)
When fossil fuels burn
efficiently in an excess of air/oxygen the main products are
carbon dioxide and water e.g.
examples of complete
combustion burning are for example natural gas and petrol
stations burn huge quantities of fossil fuels in the form of mainly coal, but
significant quantities of gas ans some oil. The heat from the very exothermic
combustion is used turn water into steam and steam driven turbines power the
electrical generators (very big dynamos!).
If there is not enough oxygen
present to completely burn the fuel to carbon dioxide and water other
products may form causing pollution and fuel inefficiency.
This is referred to as
Visually, blue flames
indicate complete combustion releasing lots of heat energy, but smokey
yellow flames indicate incomplete combustion releasing less energy.
The most common partially burned products are likely to
be carbon C (soot) and deadly carbon monoxide CO.
A simplified word
equation covering most possibilities is ...
fine black powder-dust is potentially harmful and readily formed in
fires i.e. its classically produced by smoky yellow flames and inefficient motor vehicle engines.
like any fine solid 'dust' is harmful when absorbed on the sensitive
tissue of the linings of the nose, throat and lungs.
Black sooty marks
indicate incomplete combustion and soot deposits cause
coughing and sore throat and are ejected from your body through
sneezing, coughing, and nose blowing.
Coarse particles (10 microns) are
inhaled into your windpipe and settle there, causing irritation and more
Soot is also a 'carrier' of polycyclic aromatic
hydrocarbons (PAH's) on it which are carcinogenic.
Even very low
concentrations of carbon monoxide can be fatal. Why?
Oxygen is carried
around the body by a complicated protein molecule in red blood
cells called haemoglobin.
The bonding between oxygen and
haemoglobin is quite weak to allow easy oxygen transfer for
Unfortunately, the bonding between carbon
monoxide and haemoglobin is stronger, so oxygen is replaced by
carbon monoxide and blocks normal cell respiration.
consequences are reduced blood oxygen concentration leading to unconsciousness
This is why long road
tunnels are ventilated and you should never run a car engine in a closed
appear that the hydrogen in the fuel molecules is more easily burned and
usually forms water so the equations for incomplete combustion below show
the formation of carbon-soot and 'deadly' carbon monoxide when there is a
lack of oxygen for complete combustion. Particulate carbon doesn't
get the headlines like acid rain, but it is a serious problem that
you get from burning coal and diesel fuel too.
As mentioned already, soot
is obviously a 'dirty' pollutant coating any surface (including your
lungs!) that the soot particles settle on - dark colouration on
buildings from the Industrial Revolution the emergence of steam
powered Victorian technology.
Soot particles of carbon
also contain unburned
carcinogenic hydrocarbons AND carbon monoxide is involved in the
chemistry of photochemical smogs - so all in all, inefficient
combustion of fossil-hydrocarbon fuels is very undesirable!
There is also less heat released
in incomplete combustion compared to
complete combustion since not all the carbon atoms of the fuel are
fully combined with the maximum amount of oxygen.
it is extremely important that any combustion system is as efficient as
possible e.g. gas heaters, furnaces etc. must all have excellent ventilation
for complete combustion to harmless water and carbon dioxide.
If there is any smell
of gas, make sure (i) all appliances are turned off, (ii) all sources
of ignition are absent, and (iii) ring the gas board!
appliances have led to tragic deaths.
monoxide is colourless and odourless
and even low concentrations in the air
can be fatal.
It also accounts for why
long road tunnels need to be well ventilated too to avoid any toxic
Hot water heaters, gas
fires and central heating boilers, should all be regularly serviced
to ensure they burn efficiently and not produce any potentially
harmful levels of toxic carbon monoxide.
All gas fired appliances
Carbon monoxide is unfortunately
emitted by all car exhausts, though catalytic converters help
reduce this by converting nitrogen monoxide (another pollutant) and carbon
monoxide into harmless nitrogen and carbon dioxide.
2CO(g) ==> N2(g) + 2CO2(g)
like platinum and rhodium are used in the catalytic converter.
NO, is formed by the combination of nitrogen and oxygen at high
temperature in automobile engines (cars, lorries, buses etc. - its
all the same!)
O2(g) ==> 2NO(g)
readily forms nitrogen dioxide by combining with oxygen in air on
exit from the engine exhaust.
O2(g) ==> 2NO2(g)
Nitrogen dioxide 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.
The reduction of fossil
fuel burning is the only way to reduce photochemical smog e.g. using
photovoltaic cells to harness solar energy to produce electricity.
Using solar power indirectly in this way to run electric cars is
potentially a good partial solution to the problem.
pollution problems of plastics
More on "What is produced when
organic compounds are burned"?
Some organic compounds are used as fuels.
Other organic compounds, including plastics, are
burned as waste. Burning these organic compounds releases gases into the
organic compounds consist partly of
carbon atoms and many contain hydrogen and other atoms such as oxygen and
nitrogen. Coal, crude oil, natural gas (methane) and wood
contain organic compounds
- all are used as fuels, either directly
like coal or natural gas,
- or indirectly as coke from coal or
petrol from crude oil etc.,
- and apart from wood, they are finite
(limited reserve) fossil (from decayed organic material) fuels.
- Many hydrocarbons are fuels
substance burned to release heat energy.
- When organic compounds are burned in a
plentiful supply of air the carbon is oxidised to carbon dioxide and the hydrogen
is oxidised to water.
- In a limited supply of air incomplete combustion
occurs forming carbon monoxide and/ or carbon.
- Carbon monoxide is
poisonous because it reduces the capacity of blood to carry oxygen.
- Combustion equations and tests for combustion products
are all on the Oil Notes
web page, lots of examples and diagrams too.
- Each fossil fuel has a different cost, efficiency and cleanliness
on burning. Generally speaking in 'cleanliness' the order is methane
(natural gas) > alkanes in petrol > heavy oil and from left
to right there is also an increase in C/H atom ratio in the molecule so
more CO2 produced too. Some
on other fuels (but they were designed for more advanced level
courses) and a fossil
fuel properties survey above.
- The combustion of plastics (and other organic compounds) which
contain chlorine and nitrogen produce poisonous fumes when burnt e.g.
chloride HCl and toxic hydrogen cyanide HCN respectively. Especially where there is a
limited supply of air. The combustion products of carbon (toxic CO and CO2)
and hydrogen (H2O) are
aspects of the Petrochemical Industry
Products and Environment Problems & what can we can do?
Global warming, climate change,
atmospheric pollution from fossil fuel burning
'COSTS'?: Our economy, like many
other countries has become very dependent on the extraction, sale and
use of oil based products. BUT, there is high price to be paid at
times whether it be pollution effects or warring countries with oil
The price of oil can vary
with market forces determined by the World's economy AND political
instability and wars, particularly in the major oil producing
Middle-East Arab Gulf states affect the price too.
alternative energy resources, we are at the mercy of forces beyond our
If stocks or production
rates fall, the price of crude oil rises.
Richer countries can afford
more costly oil and can stockpile it, developing countries will struggle
In order to preserve our
crude oil and gas supplies we sometimes compromise our ideals when
dealing with the politics of countries we may think unsuitable.
ACCIDENTS: Oil rig accidents,
broken pipelines, oil tanker wrecks etc. all have terrible effects on the
plant and animal life of the locality as we see from the horrible TV pictures of
seabirds coated in oil, and toxic oil slicks covering the beaches and
Birds get poisoned when
trying to clean themselves as crude oil sticks to feathers, and other animals like sea otters, whales can
be poisoned too.
In fact the whole marine
ecosystem of an area can be devastated so that even creatures not
directly poisoned can be affected if their food chain is disrupted.
Even the use of huge amounts
of detergents to break up oil slicks and disperse the pollution may
damage aquatic ecosystems too. Detergents can be toxic to some se
creatures e.g. species of fish and molluscs like shellfish.
There is also the risk to humans from fires and explosions on
rigs or at oil refinery installations and fuel storage depots etc.
RISING CARBON DIOXIDE LEVELS - greenhouse gases -
climate change - global warming
The graph shows the
steady rise in the concentration of carbon dioxide in the atmosphere
from 1959-2004 as measured at the Mauna Loa mountain top observatory on
the Pacific island of Hawaii.
In 2012 the carbon
dioxide concentration in the air has reached 400 ppm.
This represents the highest
carbon dioxide levels in the atmosphere for at least 250,000 years. This
is known because trapped air bubbles in ice cores from the arctic
regions can be analysed to obtain their % composition. Every year snow
falls form a new layer that become compacted into thin layers of ice
which become buried beneath successive yearly precipitations so a long
geological record of the earth's atmosphere is preserved.
It is a good
base-line for our planet because it is well away from any industry
involving fossil fuel burning.
The concentration of
CO2 is in ppm (parts per million).
1ppm means 1 in 106
of air molecules is CO2. In % volume terms, 1 ppm = 100 x 1 /
106 = 0.0001%.
The graph shows that
the CO2 has risen from 0.0316% (316 ppm) in 1959 to 0.0378%
(378 ppm) in 2004.
This doesn't seem
much of an increase, BUT on a global scale, the extra 'Greenhouse CO2
Gas' could have drastic consequences (see next paragraph), but the
computer model predictions have a high degree of uncertainty.
I've started a new
page of extra material including graphs, explanations and discussion points
The burning of oil and
other fossil fuels is believed to be contributing to the 'Greenhouse
There are also other
factors which may indirectly increased global warming by NOT
reducing carbon dioxide levels e.g.
Deforestation for farming
and timber, cutting down large tracts of forest is removing plants that
are absorbing carbon dioxide in photosynthesis.
Not only that, clearing
forests by burning is adding carbon dioxide to the atmosphere.
Microorganisms are also
producing carbon dioxide when they decompose dead wood.
However, burning fossil
fuels at the current rate, is still the biggest contributor to rising
carbon dioxide levels, but scientists are doing their best to try to fix
the problem and restore the balance of the carbon cycle!
Carbon dioxide from fossil fuel
burning, and other gases
including methane, water vapour and CFC's absorb the re-radiated
lower frequency infrared energy from the Earth's surface and so warming the
atmosphere, rather like a greenhouse allows the sunlight in but not
out. The effects are predicted
to be dramatic e.g. rising sea
levels as polar ice melts causing flooding in low lying land,
more energy in the global weather system leads to more frequent
violent weather patterns etc. etc.
further note from IPCC report
2007) BUT there is considerable
uncertainty as to what might actually happen, but the consensus
amongst scientists is that fossil fuel burning is raising the global temperature
by a small, but not insignificant amount.
What can we do
about it? i.e. how can we reduce our 'carbon footprint' to reduce global
amount of fossil fuels we burn in power stations, but the
international community is struggles to come to an agreement over this
issue and the huge, and fast growing economies of India and China are
demanding the building of large numbers of fossil fuel power stations
(in 2006 China is starting to build one every week!).
alternative renewable energy resources can be more exploited,
but not without problems e.g.
wind turbines -
power - subject to storm damage
damming the exit
from a valley or canyon, but who wants their valley flooded!
a large tidal
barrage across a river estuary, but what about
environmental-ecological effects, and possible silting up.
photovoltaic cells -
depends on intensity of sunlight and varies from country to
country, through the day and the seasons
solar power panels in roofs etc.
- comments as above!
reduce acid rain pollution and CO2 production by using less
good for domestic and small communities but only nuclear power and
large scale hydroelectric power schemes are
suitable for large scale energy production for the highly populated
countries with large industrial economies.
Like 2., nuclear power is another option that does not produce carbon dioxide
and is suitable for large scale power generation, but there are real
public fears about the safety of nuclear power generation 'fuelled' by
the consequences of the nuclear power plant accident
at Chernobyl, in the Ukraine in 1986. It is extremely costly to build
nuclear power stations and there are added extra long term costs in
decommissioning nuclear power stations, safely processing the waste
and safely storing the residual radioactive waste for hundreds to
thousands of years.
include storing the CO2 from fossil fuel power stations
underground in rocks under pressure - but I don't know any details
or how feasible it is.
electricity and heat energy from fuel combustion by being careful
of its use e.g. increase home insulation and more efficient electrical
appliances like 'low energy' light bulbs.
Burning wood is
sustainable and the CO2 formed on its combustion is
recycled via photosynthesis BUT (i) it does not burn cleanly, (ii) its
energy density is low (heat energy released per mass of fuel) and
(iii) no good for large scale power generation.
Using alternative fuels
like hydrogen (no CO2 formed) and carbon neutral fuels
based on biomass like ethanol, biodiesel etc. See 9b.
Biofuels & alternative fuels,
hydrogen, biogas, biodiesel
Scientists do come up
with some other interesting ideas e.g.
Much of the
photosynthesis in oceans is done by phytoplankton in the upper
layers of the ocean. One of the essential minerals these plants
need to photosynthesis is an iron. It has been suggested that
seeding parts of the ocean with a soluble iron compound will
promote the growth of plankton and absorb more carbon dioxide
via photosynthesis. However, although in principle a good idea,
you can't control which plankton grow and some of them are
toxic. These blooms of phytoplankton may become so 'thick' so
that in lower layers of the oceans, microorganisms decompose
them, using up oxygen and killing most aquatic life in the
less polluting public transport systems to reduce the number of
private cars on the roads, particularly in cities and other busy
This makes the predictions about global warming even more uncertain.
As the earth warms up, more
water vapour can exist in the atmosphere.
The more cloud that is formed in the upper atmosphere the more
sunlight is reflected, so less radiated energy reaches the Earth's
surface, leading to the opposite of global warming.
It has been
suggested that cloud formation could be encouraged by seeding the
atmosphere with crystals to promote cloud formation.
It is ironic
that the vapour trails of aircraft, with their heavy use of fossil
fuels, actually contribute to global dimming as well as to global
warming at the same time!
The effect of global dimming was noticed
in the aftermath of the 9/11 terrorist attacks on New York's World Trade Center
Twin Towers in 2001.
aircraft were grounded in the USA and many parts of the world for several days
after the attacks and
sunlight gauges showed a small but abnormal increase in sunlight levels
reaching the Earth's surface.
It is believed that
small (fine) solid particles like soot/carbon or ash in the atmosphere can cause global dimming
because they form the nuclei of water condensation producing the fine
water drops of clouds.
POLLUTION - other than the effects of carbon dioxide
There are many reasons why
we should do our best to control atmospheric pollution, and there are
plenty of examples described in the next few paragraphs.
Unless strategies are put in
place, pollutants build up and create environmental problems for most
plants and animals.
In particular, the air of
many of the world's cities is highly polluted, causing ill-health e.g
respiratory diseases like asthma.
In principle, the easiest
way to reduce pollution (or global warming) is to use less electricity,
so burning less fossil fuels, but easier said than done! Alternative
fuels and other forms of electrical energy generation are being
developed (see above discussion), but are they being developed fast
enough and to meet consumer demands?
We all like our convenient
central heating and reliance on electricity for running our homes. Just
think of al we use that runs off electricity - cooker, TV and video
systems, washing machine, shower, computers, electric blanket (its cold
on the North York Moors in winter!) etc. etc.
ACID RAIN (from sulfur
oxides and nitrogen oxides): Fossil fuels contain
compounds of the
element sulphur . When the fuel is burned the sulphur
compounds also burn
to form sulphur dioxide. This is
an acidic gas and dissolves in
rainwater, it then reacts with water and oxygen to form a very dilute solution of
sulphur + oxygen ==>
Sulphur dioxide is
a harmful gas and lung irritant and contributed to 5000 extra
deaths in the great 'London Smog' in the 1950's as well as being a
major acid-rain gas.
Sulfur dioxide reacts with oxygen (in air) and water
(rain) and gets oxidised to form very dilute sulphuric acid - the
origin of acid
rain, and the overall change is represented by the equation below.
+ O2(g-air) + 2H2O(l-rain) ==>
The formation of acid
rain has several bad effects on the environment e.g.
the low pH of acid
rain causes plant damage, inhibiting growth and killing
acid rain kills certain
life forms and so damages eco
cycles and food chains in rivers or lakes harming wildlife like trout,
'weathering' corrosion rates of building stone and statues, particularly
those made of limestone in medieval times, the industrial
revolution has devastated many of them!
Smoke from fossil fuel
power stations can be treated to remove most of the acidic sulfur
dioxide, but we do demand our electricity supply and its not always
easy to balance environmental impact versus consumer demand.
All fuels are
processed at the oil refinery to reduce the concentration of
sulfur/sulphur compounds (the process of
desulfurisation/desulphurisation) but this adds to the cost and not
all the sulphur/sulfur is removed.
However, low sulfur
content petrol and diesel are being introduced.
Of course, the less
fossil fuels we burn, the less pollution results, so strategies to
design more efficient road vehicles, using less energy in the home,
renewable energy resources etc. will all help in the long run to
Power stations can be
fitted acid gas scrubbers eg removing the acidic sulfur
dioxide with an alkaline mixture of water mixed with powdered
An alkaline slurry
(mixture of solid + powdered solid) of calcium hydroxide (calcium
oxide + water) is sprayed into the flue gases from the power station
In a neutralisation
reaction, the sulfur dioxide reacts with the calcium hydroxide to
make the neutral salt calcium sulfite - a waste product, but much of
the acidic sulphur dioxide is removed, so less acid rain damage to
The process is called
flue gas desulfurization.
POLLUTANTS: High temperature
combustion also produces other pollutants including ...
collectively denoted by NOx:
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. Many
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
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.
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
converters* can significantly reduced these three unwanted
emissions (see above for
CO and NO removal, and CxHy gets
oxidised to CO2 and H2O). * e.g. using
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:
Lead compounds are
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.
Multiple Choice Quizzes and Worksheets
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry
3 linked easy Oil Products gap-fill quiz worksheets
ALSO gap-fill ('word-fill') exercises
originally written for ...
... AQA GCSE Science
Useful products from
crude oil AND
... OCR 21st C GCSE Science
Worksheet gap-fill C1.1c Air
pollutants etc ...
... Edexcel 360 GCSE Science
Crude Oil and its Fractional distillation
... each set are interlinked,
so clicking on one of the above leads to a sequence of several quizzes
ALL my Advanced
Level Organic Chemistry revision notes
fossil fuels pollution sulfur
oxides nitrogen oxides global warming best fuel? Revision KS4 Science revising
fossil fuels pollution sulfur oxides nitrogen oxides global warming best fuel? Additional
Science Triple Award Science Separate Sciences Courses aid to fossil fuels
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