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Vehicle Emissions

Emissions from automobiles are one of the greatest contributing agents of air pollution in major cities across the globe. Driving a personal car is the most polluting activity of most citizens. Car emissions contain a range of many toxic pollutants such as sulphur dioxide, carbon monoxide, formaldehyde, nitrogen dioxide, benzene, and polycyclic hydrocarbons lead.

Combustion Process

A car is moved by burning fuel in an engine and its by-products are released in the combustion process into the surrounding environment. The by-products are released by the processes such as evaporative emissions, exhaust emissions, and refueling losses.

Perfect Combustion: The fuels like diesel and gasoline contain hydrocarbons, which is a mixture and carbon and hydrogen atoms. In the perfect combustion process, the oxygen from the air converts the hydrogen from the fuel to water and carbon into carbon dioxide, thus nitrogen in the atmosphere is left undisturbed. But, in the real combustion process, several kinds of pollutants are released in the atmosphere and create a serious impact on the environment.

Perfect combustion can be illustrated as: fuel + air = water + carbon dioxide + undisturbed nitrogen.

Normal combustion process can be illustrated as: fuel + air = nitrogen oxides + carbon monoxide + unburned hydrocarbons + water + carbon dioxide.


Carbon dioxide: Recently, carbon dioxide (CO?) was considered as the product of the perfect combustion as it is relatively harmless. Carbon dioxide does not have any direct impact on the human health, but it contributes much to the global warming. This greenhouse gas catches the earth heat and promotes global warming.

Carbon monoxide: Carbon monoxide (CO) is released as the by-product of normal or incomplete combustion process. This pollutant is formed when the carbon from the fuel is oxidized partially and this by-product has serious impact on the human health. Carbon monoxide affects the oxygen in the blood flow and creates major impact on an individual with the heart disease.

Hydrocarbons: Hydrocarbon pollutants are formed when the fuel is not completely burned. These unburned hydrocarbons react with nitrogen oxides to form ground-level ozone, which is a major contributor of smog formation. Hydrocarbons create various health problems such as eyes irritation, respiratory problems, and lungs damage. These hydrocarbons are the agents for many urban air pollution problems and also one of the potential causes of cancer.

Nitrogen oxides: The oxides of nitrogen are formed when the nitrogen and the oxygen react under very high temperature and pressure in an engine. These pollutants are the causative agent of the acid rain and precursors to the ozone formation.


Some hydrocarbon pollutants mix in the air through evaporation of fuel. These evaporative fuel emissions can occur in several methods such as: refueling, hot soak, and diurnal.

Refueling: The vapors of gasoline are normally present in the fuel tank and they are forced to release when the fuel tank is refueled.

Hot Soak: The engine of a car remains hot for a small period even after the car is switched off and evaporation of gasoline continues while cooling down.

Diurnal: In this method, the evaporation of gasoline continues and increases when the car is parked. This occurs due to the rise of temperature during the day.

  • Automobile Emissions: Here, sources of car emissions, combustion process, and exhaust pollutants are given in an understandable format.
  • Vehicle Emissions: Here, exhaust emissions, evaporative emissions, trip emissions, and car and truck emissions are clearly explained.
  • Automobile Emissions: Here, automobile emission acts and ways of packaging waste in the European Union and the United States are given.

Preventive Measures for Car Pollution and Emissions

The Clean Air Act gave the EPA required authority to regulate the automobile pollution. The standards and policies of EPA states the amount of pollution an automobile can emit. The emission reduction standards formed in 1970 introduced basic engine improvements, adding charcoal canisters to collect vapors of hydrocarbon, and recirculation valves to limit the formation of nitrogen oxides.

The introduction of catalytic converters in 1975 helped in limiting the carbon monoxide and hydrocarbon emissions. Also, introduction of unleaded gasoline helped in reduction of lead levels in the environment. In 1980-81, due to the strict standards, car manufacturers introduced new cars with advanced emission control systems. This new emission control systems contain a three way catalyst, on-board computer, and oxygen sensor.

In addition, malfunctioning of emission controls are identified efficiently by computerized diagnostic systems and advanced evaporative emission controls.

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