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Origins and environmental implications of pollutants in car exhaust gases

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Ellis Skinner

on 16 December 2012

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Transcript of Origins and environmental implications of pollutants in car exhaust gases

What are the origins and environmental implications of pollutants in car exhaust gases? The trouble with emissions Unburnt hydrocarbons CARBON MONOXIDE There are slight differences between the emissions of petrol and diesel engines . However there are many of pollutants in both, e.g the nitrogen oxides (NO), and the sulfur oxides (SO).

One of the main problems is the volatility of petrol, on warm days, motor vehicles give off hydrocarbon fumes, mostly butane (C4H10) from the petrol tank and carburettor. This is described as EVAPORATIVE EMISSION, and is responsible for roughly 10% of emissions of volatile organic compounds from petrol vehicles. The problems with Unburnt Hydrocarbons Hydrocarbons, when they are a vaporized in car engines and pollute the atmosphere, are toxic, in very high concentrations attacks the lung tissue, and carcinogenic (have the potential to cause cancer) to humans.
Also, when they are in the atmosphere they react with nitrogen oxides, oxygen and water vapor if the come into contact with sunlight. They create ozone in this reaction. Ozone in the troposphere (rather than the insulating layer in the stratosphere) acts as a green house gas, causing global warming

[source: Environmental protection agency] Q: What are they?
A: The incomplete combustion of octane in petrol will cause unburnt hydrocarbons together with carbon monoxide with water. They escape into the the atmosphere together with octane (unburnt hydrocarbon) UNBURNT HYDROCARBONS The problems with carbon monoxide Carbon monoxide is formed by the incomplete combustion of hydrocarbon fuels. It is very toxic to humans,Inhaling the gas reduces the blood's ability to carry oxygen, leaving the body's organs and cells starved of oxygen. Also it is oxidized into carbon dioxide in the atmosphere


C3H8 (g) + 3.5 O2 (g) ----> 3 CO (g) + 4 H2O (g)

[source: Chemical Ideas] Particulates What are particulates, and how are they formed? A: Particulates are very small nanoparticles (1-100nm) which are distibuted by the exhaust gases from cars and can get into our lungs and cause irritation. Particulates are also formed by the incomplete combustion of the hydrocarbon fuels in diesel.

e.g. C12H23+11.75O2=12CO+11.5H2O

What are the health problems involved with Particulates? Numerous scientific studies have linked particle pollution exposure to a variety of problems, including:-premature death in people with heart or lung disease,-nonfatal heart attacks,-irregular heartbeat
-aggravated asthma,-decreased lung function, and-increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing.

Source : EPA(environmental protection agency) Carbon dioxide How does Carbon dioxide form in car engines? Carbon dioxide forms in two was in car engines, Mainly it forms from the complete combustion of the hydrocarbon fuel ( a mix of iso-octane and heptane)
e.g. 2C2H6 + 7O2 ----> 4CO2 + 6H2O

However, Carbon dioxide is also formed by catalytic converters in car engines : these change the more harmful Nitrogen oxides and Carbon monoxide into the less harmful Carbon dioxide:

2CO + 2NO N2 + 2CO2 Environmental problems of carbon dioxide To Humans , CO2 is a poison and breathing too much is toxic.

Too much in the atmosphere causes too thick a layer of photochemical smog (insulation around the earth) . Carbon particles absorb heat like little bricks, for example: It has a Specific heat capacity of 0.819 KJ/KgK , in comparison Air has a specific heat capacity of 1.005 KJ/kgK . So the sun's heat warms the carbon and radiates the heat down to the earth. The heavier the layer of carbon the more heat provided as an insulation, preventing some heat from bouncing back into space.

S.H.C source : the engineering toolbox . com Nitrogen Oxides (NOx) Q: What are they and how are they formed? The most important forms of reactive nitrogen in the air are nitrogen monoxide (NO) and nitrogen dioxide (NO2) and together we call them NOx.

Because the two nitrogen atoms in N2 are bound very strongly together (with a nitrogen to nitrogen triple bond), it isn't easy to break N2 down into its atoms.

Vehicle engines operate at high enough temperatures and nitrogen oxides are emitted in the exhaust fumes.

They are mainly formed from components of the air itself. at the high temperatures of vehicles' engines, the nitrogen and oxygen react to form NO, some of which reacts with oxygen to form NO2

N2 + O2 --------> 2NO Environmental problems with Nitrogen oxides: Oxides of nitrogen are acidic (for example Nitric acid has a pH of 1.0 , for a normality of 0.1 mol/ L) , and gives rise to acid rain in the atmosphere. This can cause health problems, particularly asthmatics, it can also corrode limestone buildings and damage forests and lakes)
[pH source: engineering toolbox . com] Sulfur Dioxide How is sulfur dioxide formed in car engines? The oxides of sulfur in vehicle exhaust fumes come from sulfur compounds in the fuel. These then combine with oxygen in the heat of the engine. Once again, the S2 Bonds require a lot of energy to break, (421.3 KJ/Mol) and so sulfur oxides can only be formed under the heat of car engines (roughly 1000 degrees C)

S(s) + O2(g) SO2(s)

[bond enthalpy source: the engineering toolbox.com] What problems does sulfur dioxide cause for us? - Again, like Nitrogen oxides, the sulfur oxides are acidic and so contribute towards acid rain.
- Sulphur dioxide can cause respiratory problems, such as bronchitis, and it can irritate your nose, throat and lungs. It may cause coughing, wheezing, phlegm and asthma attacks.
- Sulphur dioxide deposition can affect vegetation around industrial discharges and in cities.
- Finally, Sulphur dioxide can form secondary particles (sulphates) that cause haze and reduce visibility. In Conclusion Combustion of hydrocarbon fuels in cars creates masses of harmful substances that impact the environment, and can also cause us ourselves major health problems.
Despite efforts, such as the implication of the catalytic converter, Pollution form car exhaust gases still proves to be one of the major contributors to greenhouse gases today.
One of the main reasons for this is that the average journey length is roughly 5 miles. Unfortunately catalytic converters need a minimum of 6 miles to be driven before they start to work efficiently (this is because the active site on the catalyst needs to be hot before it can attract the exhaust gas molecules) Hence why exhaust gases are still a major contributor to the greenhouse effect today
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