<p class="MsoNormal"><span style="font-size: 1rem;">Hello, great readers. Greetings to the entire
steemstem and stem communities. Thanks for the constant support and motivation.
Today, I will continue from where I stopped in my previous post on </span><a href="https://www.steemstem.io/#!/@empressteemah/alkanes-the-car-engi-1581946672" target="_blank">ALKANES, THE CAR ENGINE AND ATMOSPHERIC POLLUTION</a><span style="font-size: 1rem;">. I will be discussing on octane number of
a petrol blend, blending an unleaded petrol, the greenhouse effect from
pollution and some other interesting topics relating to alkane and atmospheric
pollution.</span></p><p class="MsoNormal"><div style="text-align: center;"><img src="https://res.cloudinary.com/drrz8xekm/image/upload/v1582303034/g3kkr2tirvjpnuozxf2v.jpg" data-filename="g3kkr2tirvjpnuozxf2v" style="font-size: 1rem; width: 527.528px;"><a href="https://pixabay.com/photos/fuel-pump-energy-gas-pump-1596622/" target="_blank"><sup>Fuel pump. Image by IADE-Michoko from Pixabay</sup></a></div><br></p><h2><span lang="">OCTANE NUMBER OF A PETROL BLEND<o:p></o:p></span></h2><p class="MsoNormal"><span lang="">As the petrol-air mixture is compressed in a
cylinder, it becomes hot and sometimes ignites without the aid of a spark from
the spark plug (auto ignition). When this happens, the fuel does not burn
smoothly, but explodes in different parts of the cylinder, which generates a
rapid knocking noise. Knocking can damage the cylinder and piston head and,
because the petrol-air mixture does not ignite at the right time, it leads to a
loss of power and inefficient use of fuel.<o:p></o:p></span></p><p class="MsoNormal"><span lang="">It is the job of the petrol blender to produce
a knock-free fuel, So blenders use a measure of a blended petrol’s resistance
to knocking, call octane number. Remember that 2,2,4-trimethylpentane used to
be known as iso-octane, which is why the scale is called octane number or
octane rating. Branched-chain alkanes burn more smoothly in an engine than straight-chain
alkanes. 2,2,4-Trimethylpentane has a low tendency to a ignite when compressed and
is given an octane number of 100. The unbranched chain alkane heptane knocks
readily, even under mild compression. It is given an octane number of 0.
Mixtures of these two alkanes are used to assign octane numbers to petrol
blends. So if, under test conditions, a particular petrol blend knocks at the
same compression as a mixture of 90 per cent 2,2,4-trimethylpentane and 10 per
cent heptane, the octane number of that petrol blend is 90.</span></p><p class="MsoNormal" style="text-align: center; "><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/0/0f/Gas_Station_Pump_Five_Octane_Ratings.jpg/550px-Gas_Station_Pump_Five_Octane_Ratings.jpg" style="width: 527.528px;"><span lang=""><o:p><br></o:p></span></p><p class="MsoNormal" style="text-align: center; "><a href="https://commons.wikimedia.org/wiki/File:Gas_Station_Pump_Five_Octane_Ratings.jpg" target="_blank"><sup>A US gas station pump offering five different (R+M)/2 octane ratings. Bobak at English Wikipedia, CC BY-SA 2.5</sup></a><span lang=""><o:p><br></o:p></span></p><h2><span lang="">ADDING LEAD COMPOUNDS TO PETROL<o:p></o:p></span></h2><p class="MsoNormal"><span lang="">The advantage of high-octane fuels is that
they can be highly compressed, which gives more power per piston stroke and a
more efficient use of fuel. In the 1920s, it was discovered that adding small
amounts of a certain lead compound to petrol significantly increased the octane
number, a practice that was adopted by all the major petrol suppliers.<o:p></o:p></span></p><p class="MsoNormal"><span lang="">However, the use of lead in petrol to raise
the octane number is now banned in most countries for two reasons, both of them
connected to the pollution of the environment by lead discharged through exhausts.
The first is that lead is a poison that accumulates in the bodies of humans and
other animals. Evidence suggests that when children breathe in airborne lead,
their IQ level is liable to be lowered, and for adults, their ability to
concentrate is reduced. Since the advent of unleaded petrol in the UK in 1986,
the concentration of airborne lead in the environment has been reduced by 80
per cent. The second reason why leaded petrol is being phased out is that it
inhibits the action of catalysts in catalytic converters, which are essential
to reduce pollution from vehicle exhausts.<o:p></o:p></span></p><h2><span lang="">Blending unleaded petrol<o:p></o:p></span></h2><p class="MsoNormal"><span lang="">If lead is not used to improve the octane
number, an alternative way must be found. One solution is to dissolve into the
blended petrol small straight-chain alkanes such as butane. The shorter the
chain, the less likely is auto-ignition of the mixture. As the alkane chain
becomes longer, so the tendency to auto-ignite increases and the octane number
decreases. However, too many short-chain alkanes with low boiling points increase
the volatility of the petrol too much. This could lead to vapour lock, and it
increases evaporation of hydrocarbons from the fuel tank and engine – yet
another source of atmospheric pollution.<o:p></o:p></span></p><p class="MsoNormal"><span lang="">Using branched-chain alkanes is another way to
raise the octane number of petrol. The more branched the chain, the higher its
octane number. Branched-chain alkanes are produced at the refinery by cracking
and reforming reactions.<o:p></o:p></span></p><p class="MsoNormal"><span lang="">A third way is to add aromatic hydrocarbons.
Some 40 per cent of the petrol used in the UK contains such additives. One of them
is benzene, a known carcinogen (cancer-causing agent), which can make up to 5
per cent by volume of a petrol. Benzene is now being linked to childhood leukaemia,
and is thought to be the major cause in some cases. The level of benzene inside
a car can be up to ten times higher than outside.<o:p></o:p></span></p><p class="MsoNormal"><span lang="">The octane number can also be improved by
adding oxygenates. Oxygenates are partly oxidised fuels that already contain
oxygen in their molecules. Methanol (CH<sub>3</sub>OH) has an octane number of
114 and ethanol (C<sub>2</sub>H<sub>5</sub>OH) is 111, so they burn smoothly
under high compression. Also, because they have an oxygen atom already in the
molecule, when they are combusted they require less oxygen in the petrol-air mixture.
So petrols that contain oxygenates produce less carbon monoxide when burnt.</span></p><p class="MsoNormal" style="text-align: center; "><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/0/0b/2012_Camry_fuel_filler_cap_04_2014_141619.jpg/640px-2012_Camry_fuel_filler_cap_04_2014_141619.jpg" style="width: 527.528px;"><span lang=""><o:p><br></o:p></span></p><p class="MsoNormal" style="text-align: center; "><a href="https://commons.wikimedia.org/wiki/File:2012_Camry_fuel_filler_cap_04_2014_141619.jpg" target="_blank"><sup>2012 Toyota Camry Hybrid fuel filler cap showing warning regarding the maximum ethanol blend allowed by the carmaker, up to E10 gasoline. The warning label indicates that ethanol blends between E15 to E85 shall not be used in this vehicle. Mariordo (Mario Roberto Durán Ortiz), CC BY-SA 3.0</sup></a><span lang=""><o:p><br></o:p></span></p><h2><span lang="">POLLUTION FROM VEHICLES AND CATALYTIC CONVERTERS<o:p></o:p></span></h2><p class="MsoNormal"><span lang="">At the outset of this chapter, I pointed to the
problem of vehicle emissions. Now I’m going to look in more detail at the
chemistry behind the pollution associated with the burning of hydrocarbon
fuels, such as petrol in vehicle engines. Pollution such as: Carbon dioxide
increasing the greenhouse effect, carbon monoxide being toxic to all
vertebrates. Nitrogen oxides causing respratory problems and acid rain. Unburnt
hydrocarbons helping to form photochemical smog and some causing cancer. Suphur
oxides causing acid rain, uncontrolled exhaust emissions cause increasing concern,
etc. <o:p></o:p></span></p><h2><span lang="">CARBON DIOXIDE AND THE GREENHOUSE EFFECT<o:p></o:p></span></h2><p class="MsoNormal"><span lang="">When a hydrocarbon completely combusts, it
produces just two products: carbon dioxide and water. Both of these are referred
to as greenhouse gases, but what are greenhouse gases and how did they get
their name?<o:p></o:p></span></p><p class="MsoNormal"><span lang="">The atmosphere of the Earth acts like glass in
a greenhouse. For a start, the atmosphere reflects 30 per cent of the Sun’s
energy back into space. The remaining 70 per cent, which is mainly visible
spectrum light, passes through the atmosphere to strike the Earth. Some of this
energy is used by plants for photosynthesis, and some is used to evaporate water
from the oceans, lakes and vegetation, but most of it warms the surface of the
planet. The warm Earth’s surface in turn emits its own radiation, and this is
where certain gases in the atmosphere act like greenhouse glass. The energy radiated
by the Earth’s surface is in the long-wave infrared (IR) region of the
spectrum. The greenhouse gases absorb this IR radiation, and their molecules
become excited.<o:p></o:p></span></p><p class="MsoNormal"><span lang="">Three of the most important greenhouse gases
are water, carbon dioxide and methane. Quanta of infrared radiation are
absorbed by O-H, C=O and C-H bonds, which increase their vibration and thus
promote them to higher vibrational energy levels. When they fall back to a
lower vibrational energy level, they radiate these quanta of energy in all directions.
Some of this energy is transferred through collision of air particles
increasing their kinetic energy and warming the atmosphere, but the rest is
transmitted back to the Earth’s surface. This is the greenhouse effect. Let’s
be reminded that a quantum is an indivisible unit or packet of radiation energy
(also called a photon). A molecule can exist only in certain fixed vibrational energy
levels. When it absorbs a quantum of energy, it becomes excited and jumps to a
higher energy level. In this level, it vibrates more. This is similar to
electrons absorbing quanta of energy and moving to higher electron energy levels.</span></p><p class="MsoNormal" style="text-align: center; "><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/0/0a/RHSGlasshouse.JPG/640px-RHSGlasshouse.JPG" style="width: 527.528px;"><span lang=""><o:p><br></o:p></span></p><p class="MsoNormal" style="text-align: center; "><a href="https://commons.wikimedia.org/wiki/File:RHSGlasshouse.JPG" target="_blank"><sup>A modern Greenhouse in RHS Wisley. Mark Boyce , CC BY-SA 3.0</sup></a><span lang=""><o:p><br></o:p></span></p><h3><span lang="">Why we need the greenhouse effect in moderation<o:p></o:p></span></h3><p class="MsoNormal"><span lang="">If carbon dioxide and water were not present
in the atmosphere, the Earth would be many degrees cooler. We only have to look
at our two closest planetary neighbours to see the effect of greenhouse gases.
Venus has an extremely dense atmosphere, 90 times denser at the surface than
that of Earth. It is 96 per cent carbon dioxide and keeps the temperature on
Venus to a scorching 450 °C. The atmosphere of Mars has about the same
proportion of carbon dioxide as that on Venus, but is only 1 per cent as dense
as the Earth’s atmosphere. Mars is further from the Sun than Venus so you would
expect Mars to be cooler, but it has greater temperature fluctuations and cools
during its night to -80 °C because there are not enough carbon dioxide molecules
to trap the IR radiation.</span></p><h3><span lang="">The greenhouse effect and climate change<o:p></o:p></span></h3><p class="MsoNormal"><span lang="">In 2007 there were about 2850 gigatonnes of
carbon dioxide in the Earth’s atmosphere, but its concentration in air is small
at 0.0383 per cent, or 383 parts per million (ppm) by volume. We know from
analysing polar ice cores that the atmospheric concentration of carbon dioxide
has varied between 180 ppm and 300 ppm during the last 650 000 years, and at
the beginning of the Industrial Revolution, 250 years ago, there were about 280
ppm of carbon dioxide. Most of the increase in carbon dioxide concentration we
see today has happened in the past 50 years. This is clearly shown below which is one of the most important graphs in history, produced from results of
the Mauna Loa Observatory in Hawaii.<o:p></o:p></span></p><p class="MsoNormal"><span lang="">At present, the rate of increase in carbon dioxide
is about 2 ppm per year, which means that about 14 Gt is added to the
atmosphere (Gt is called a gigatonne which is 10<sup>9</sup> tonnes). However,
more than 28 Gt of carbon dioxide is produced each year, much of it from
burning fossil fuels for electricity generation or transport. So, where does
half the carbon dioxide go? Some is removed by plants during photosynthesis,
and a lot more dissolves in the oceans, lakes and waterways, but there is
evidence that oceans are absorbing less CO<sub>2</sub> than they did a few
years ago. Something that removes carbon in the form of carbon dioxide is known
as a sink. So plants and open waters are sinks for carbon. Crude oil is another
sink for carbon, and so are the bodies of animals. The amount of time carbon
spends in a sink is known as the residence time. Carbon capture and storage is
the name given to the removal of waste carbon dioxide. It can be liquefied and
injected deep into the oceans. Carbon dioxide can also be stored in geological
formations. This is happening now in some of the Norwegian oil fields that have
come to the end of their production. It can also be reacted with metal oxides
to form stable carbonate minerals.</span></p><p class="MsoNormal" style="text-align: center; "><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/c/c5/Mauna_Loa_CO2_monthly_mean_concentration.svg/480px-Mauna_Loa_CO2_monthly_mean_concentration.svg.png" style="width: 480px;"><span lang=""><br></span></p><p class="MsoNormal" style="text-align: center; "><a href="https://commons.wikimedia.org/wiki/File:Mauna_Loa_CO2_monthly_mean_concentration.svg" target="_blank"><sup>The Keeling Curve of atmospheric CO2 concentrations measured at Mauna Loa Observatory. Delorme, CC BY-SA 4.0</sup></a><span lang=""><br></span></p><p class="MsoNormal"><span lang="">Recognizing that global climate change could
result from increasing concentrations of greenhouse gases in the atmosphere,
the World Meteorological Society and the United Nations established the Intergovernmental
Panel on Climate Change (IPCC) in 1988. This organisation assesses all the
evidence from thousands of scientists researching into climate change, in order
to come to conclusions. Its latest report was produced in 2007. On the eve of
its publication, the Paris authorities switched off the lights around the city
to acknowledge the seriousness of the report’s findings. The report says that
it is 90 per cent certain that human activities are causing global warming and
climate change. This was important because many scientists in the past have
argued that global warming is part of a natural cycle and not the result of
human activity. For its work the IPCC was awarded the Nobel Prize, together
with former US Vice President Al Gore, who has also done much to publicise the
worrying implications of climate change.<o:p></o:p></span></p><p class="MsoNormal"><span lang="">The Kyoto Protocol was the first international
attempt at curbing greenhouse gas emissions. It was hammered out in 1997 at the
city in Japan in that bears its name. It committed industrialised nations to
legally binding targets to limit the emissions of six greenhouse gases (most
important being carbon dioxide) to 5.2 per cent below their 1990 levels by the
period 2008-2012. In 2005 the Kyoto Protocol came into force when sufficient countries
had signed up to account for 55 per cent of the 1990 carbon dioxide emissions.
The number of countries that have now signed is more than 141, but significantly
the USA and Australia refuse to support the agreement. The USA alone previously
accounted for almost one-quarter of all carbon dioxide emissions. This country
was the biggest emitter of carbon dioxide until it was overtaken by China,
which was building two coal-fired power stations each week in 2007. However, it
would be unfair for developed countries to point the finger at China. The
average Chinese person emits 3.5 tonnes of carbon dioxide per year, compared
with the average Briton who emits 10 tonnes or the average US citizen who emits
20 tonnes.<o:p></o:p></span></p><p class="MsoNormal"><span lang="">The situation is now considered very urgent and
many scientists believe that political action is falling a long way short of
what is needed to avert lasting damage to Earth’s climate.<o:p></o:p></span></p><h2><span lang="">REFERENCES</span></h2><p><a href="https://www.researchgate.net/post/How_to_find_the_octane_number_of_a_blended_fuel_Ex_gasoline-ethanol_blends_of_various_proportions_of_ethanol" target="_blank">https://www.researchgate.net/post/How_to_find_the_octane_number_of_a_blended_fuel_Ex_gasoline-ethanol_blends_of_various_proportions_of_ethanol</a><br></p><p><a href="https://en.wikipedia.org/wiki/Octane_rating" target="_blank">https://en.wikipedia.org/wiki/Octane_rating</a><br></p><p><a href="https://www.pei.org/wiki/octane-number" target="_blank">https://www.pei.org/wiki/octane-number</a><br></p><p><a href="http://www.todayifoundout.com/index.php/2011/11/why-lead-used-to-be-added-to-gasoline/" target="_blank">http://www.todayifoundout.com/index.php/2011/11/why-lead-used-to-be-added-to-gasoline/</a><br></p><p><a href="https://en.wikipedia.org/wiki/Tetraethyllead">https://en.wikipedia.org/wiki/Tetraethyllead</a><a href="https://en.wikipedia.org/wiki/Tetraethyllead" target="_blank"></a></p><p><a href="https://www.toppr.com/ask/question/why-is-lead-compound-added-to-petrol/" target="_blank">https://www.toppr.com/ask/question/why-is-lead-compound-added-to-petrol/</a><br></p><p><a href="https://en.wikipedia.org/wiki/Gasoline" target="_blank">https://en.wikipedia.org/wiki/Gasoline</a><br></p><p><a href="https://www.sciencedirect.com/science/article/pii/S0960148109000585" target="_blank">https://www.sciencedirect.com/science/article/pii/S0960148109000585</a><br></p><p><a href="https://www.sciencedirect.com/science/article/pii/S0196890402001668" target="_blank">https://www.sciencedirect.com/science/article/pii/S0196890402001668</a><br></p><p><a href="https://en.wikipedia.org/wiki/Catalytic_converter" target="_blank">https://en.wikipedia.org/wiki/Catalytic_converter</a><br></p><p><a href="https://www.explainthatstuff.com/catalyticconverters.html" target="_blank">https://www.explainthatstuff.com/catalyticconverters.html</a><br></p><p><a href="https://eurekalert.org/pub_releases/2000-08/ACS-Ccfo-1608100.php" target="_blank">https://eurekalert.org/pub_releases/2000-08/ACS-Ccfo-1608100.php</a><br></p><p><a href="https://www.sciencenewsforstudents.org/article/explainer-co2-and-other-greenhouse-gases" target="_blank">https://www.sciencenewsforstudents.org/article/explainer-co2-and-other-greenhouse-gases</a><br></p><p><a href="https://en.wikipedia.org/wiki/Greenhouse_gas" target="_blank">https://en.wikipedia.org/wiki/Greenhouse_gas</a><br></p><p><a href="https://climatekids.nasa.gov/greenhouse-effect/" target="_blank">https://climatekids.nasa.gov/greenhouse-effect/</a><br></p><p><a href="https://sciencing.com/importance-greenhouse-effect-3535.html" target="_blank">https://sciencing.com/importance-greenhouse-effect-3535.html</a><br></p><p><a href="http://theconversation.com/remind-me-again-how-does-climate-change-work-46" target="_blank">http://theconversation.com/remind-me-again-how-does-climate-change-work-46</a><br></p><p><a href="https://archive.ipcc.ch/organization/organization_history.shtml">https://archive.ipcc.ch/organization/organization_history.shtml</a></p><p><a href="https://www.ipcc.ch/about/history/" target="_blank">https://www.ipcc.ch/about/history/</a><br></p>