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What are Car Emissions?

Claudette M. Pendleton
Claudette M. Pendleton

Simply put, car emissions are any fumes that come out of car engines during driving. They are almost always byproducts of gasoline combustion. Most modern cars operate with engines that are powered in whole or part with gasoline, which must be burned to provide power. The fumes are usually made up of three main components: carbon dioxide, nitrogen gas, and water vapor. A number of potentially more toxic gasses are also included in most cases, though, which can make the emissions — sometimes also called “exhaust”— much more harmful. People who are exposed to concentrated inhalation can experience serious brain injury and even death. Many scholars also say that the cumulative effect of car exhaust around the world has contributed to smog and global warming, also called climate change. Governments in most parts of the world require auto manufacturers to mitigate emissions, usually through technology like filters or more efficient engine combustion chambers, to reduce the chance of harm. Drivers are also often responsible for maintaining certain “acceptable” emissions levels in their own cars.

How They Happen

The EGR valve recirculates vapors to help prevent excess nitrogen oxide from being released in a car's emissions.
The EGR valve recirculates vapors to help prevent excess nitrogen oxide from being released in a car's emissions.

Emissions happen as a normal result of gas combustion. Any time something burns, there’s almost always smoke of some sort. The smoke is made up of some of the key chemical components of whatever it is that is being burned, combined with water, oxygen, and other elements present naturally in the air. Car emissions are no different. When a car ignition switches “on,” a small spark lights gasoline in the tank on fire, which produces heat and energy that the car uses to enable its electrical and mechanical processes. Emissions are the smoke that results as the gas burns off.

Main Components

Car emissions contribute to air pollution.
Car emissions contribute to air pollution.

A lot of the specific emission composition depends on the type of fuel being burned, as well as the environmental specifics. Carbon dioxide (CO2), nitrogen gas (N2), and water vapor (H2O) are the most common components. Carbon dioxide is a product of combustion; the oxygen in the air is bound to the carbon within the fuel. Nitrogen gas is an odorless, colorless, tasteless, and mostly motionless gas, which makes up approximately 78 percent of the Earth's air. Water vapors are also a product of combustion, and happens as oxygen binds to the hydrogen within the fuel.

These most common components are by no means the only ones. Some of the more dangerous car emissions include carbon monoxide (CO), nitrogen oxides (NO), and hydrocarbons, which are also referred to as volatile organic compounds (VOC). Catalytic converters have been introduced by many manufacturers for the purpose of reducing the more dangerous emissions that car engines produce.

Health and Environmental Concerns

Carbon monoxide is usually considered one of the most dangerous gasses, at least from a human life perspective. It is a colorless, odorless, and poisonous gas. Nitrogen oxides (NO and NO2, or when combined called NOx) create problems in the atmosphere such as acid rain and smog; nitrogen oxides also contribute to many of the mucus membrane problems that a lot of people have, including allergies and asthma.

Hydrocarbons, or volatile organic compounds, are chief contributors to smog. The smog created from hydrocarbons is produced primarily from dissolved or evaporated fuel that has not been burnt. Many scholars and researchers have concluded that increased layers of smog have contributed to an inflated and unnatural insulation covering much of the earth, which can trap sunlight and raise ambient temperatures. This has been widely speculated as a cause of the melting polar ice caps and increased incidents of severe weather around the world.

It has also been speculated that emissions can eat away at the ozone layer, which is an atmospheric layer that, among other things, blocks many of the sun’s most harmful rays from reaching the earth. Holes or weak spots in the ozone can lead to a number of different problems.

Mitigation Tactics

Modern cars in most places are carefully designed with the intention of managing the quantity of fuel that is burned by maintaining the air-to-fuel ratio as close to a certain point as possible. This point is usually referred to as the “stoichiometric point,” and is believed to be the best ratio of air to fuel possible. The fuel is burned and uses all of the oxygen in the air when it is at this point. Fuel mixture varies significantly from the model ratio when driving, however.

Many different national governments have also set requirements for engine efficiency for the cars, trucks, and other automobiles that are sold within their borders or sometimes even operated on their roads. In addition, drivers in many places must have their cars tested for specific emission outputs on a regular basis. Cars that fail the set guidelines often have to be repaired to lessen exhaust, and drivers also sometimes have to pay a fine.

In addition to regular maintenance and repairs, some of the things that drivers can do to reduce emissions include avoiding unnecessary driving, driving their cars sensibly, and using what’s known as “clean” fuels. Implementing these strategies might also help drivers save money and keep their cars running longer and more efficiently.

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Discussion Comments


Car exhaust is right in our faces - not in a distant power plant, which is why it is important that we tax all emissions.


I would just like to ad that the nitrogen and co2 from car emissions is definitely a contributor to global warming and climate change. While these gases may be abundant in the atmosphere, the balance of these molecules is very important. The concentrations of these molecules in the atmosphere have also increased beyond levels ever seen in the natural cycles of atmospheric gases. It is also a tough sell to try and claim that this increase of emissions is not due to anthropogenic causes since we have been in a relatively gentle climate cycle for the last forty thousand years, and the spike coincides with the exponential increase in human populations.


@ Kamekazi- Sadly enough, few areas have restrictions on idling vehicles. Most of the places that do have restrictions are places concerned with sustainability, and densely populated urban areas. I would like to point out that most people idle their cars out of a lack of knowledge. Almost all cars built in the last twenty years do not need to warm up, so idling a car has little to no use. Even in winter, it is recommended that a car warm up under normal driving conditions.

Obviously, there are people who idle cars for the comfort that a warm car offers, but in the end, it is better to warm a car up under normal operating conditions. It will save wear and tear on the engine since it is not running as often, and it will save money on oil and fuel costs. Think about all the people who idle their cars for ten or more minutes to take a one or two mile trip. Their odometer only says they are running their vehicle for one or two miles, but for wear and tear concerns, the vehicle has been under operation for three or four times as long.


We live in a residential complex where the complex is quite enclosed with little air circulating on ground level. Some people have the habit of idling their cars for considerable periods to warm up their engine with the result that these emissions enter the units. Surely this habit is unhealthy and cannot be legal.

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    • The EGR valve recirculates vapors to help prevent excess nitrogen oxide from being released in a car's emissions.
      By: Negaro Imaging
      The EGR valve recirculates vapors to help prevent excess nitrogen oxide from being released in a car's emissions.
    • Car emissions contribute to air pollution.
      By: rob245
      Car emissions contribute to air pollution.