Brian Barton
Cars are a major contributor to air pollution, with over 1.45 billion petrol and diesel vehicles on the road globally. Cars emit a range of harmful chemicals, including carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), and hydrocarbons (HC). These emissions can reduce air quality, particularly in densely populated cities, and are a significant factor in global warming and climate change. Domestic transport accounts for 28% of total greenhouse gas emissions, with tailpipe emissions from cars, trucks, and buses contributing to over one-fifth of the United States' global warming pollution.
| Characteristics | Values |
|---|---|
| Carbon dioxide (CO2) | 4.6 metric tons per year |
| Carbon monoxide (CO) | |
| Nitrogen oxides | |
| Nitric oxide (NO) | |
| Nitrogen dioxide (NO2) | |
| Hydrocarbon fuel | |
| Methane (CH4) | |
| Nitrous oxide (N2O) | |
| Hydrofluorocarbon (HFC) | |
| Volatile organic compounds (VOCs) | Benzene, Acrolein |
| Semi-volatile organic compounds (SVOCs) | Phthalates, Polybrominated diphenyl ethers (PBDEs) |
| Particulate matter (PM) | PM 2.5, Ultrafine particles (UFP), Black carbon (BC) |
| Ozone | |
| Oxides of nitrogen |
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What You'll Learn
- Carbon dioxide, a greenhouse gas, is emitted from burning fuel
- Carbon monoxide is a toxic, invisible gas from incomplete combustion
- Nitrogen oxides are reddish-brown gases that irritate the lungs
- Sulfur dioxide is a colourless gas from burning crude oil
- Hydrocarbons are unburnt fuel that escapes from exhausts
Carbon dioxide, a greenhouse gas, is emitted from burning fuel
Carbon dioxide (CO2) is a greenhouse gas emitted from burning fuel in car engines. It is one of the main pollutants released in car exhaust, along with carbon monoxide (CO), unburned hydrocarbon fuel, and nitrogen oxides, such as nitric oxide (NO) and nitrogen dioxide (NO2). These emissions contribute to global warming and climate change, with domestic transport being the largest contributor to total greenhouse gas emissions in some countries.
The amount of carbon dioxide emitted by a car depends on several factors, including the type of fuel, fuel economy, and the number of miles driven. On average, a typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year. To put this into perspective, one pound of carbon dioxide is equivalent to approximately 231 liters or 115.5 two-liter bottles.
While car manufacturers have made efforts to reduce exhaust emissions through improved engine and exhaust system design, as well as the use of catalytic converters and particulate filters, vehicles continue to contribute significantly to air pollution. This is particularly evident in urban areas with high traffic congestion, where the emissions from millions of vehicles on the road each day add up to a substantial amount of pollution.
In addition to carbon dioxide, automobiles using gasoline also produce methane (CH4) and nitrous oxide (N2O) from the tailpipe, and all vehicles can emit hydrofluorocarbon (HFC) from leaking air conditioners. Electric vehicles (EVs) have been introduced as a more environmentally friendly alternative, as they do not emit any tailpipe emissions. However, they still produce a small amount of greenhouse gas emissions due to air conditioner/HFC leakage.
To further reduce emissions, individuals can opt for carpooling or choosing more fuel-efficient vehicles, while manufacturers continue to work on improving fuel efficiency and engine power without compromising emission levels.
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Carbon monoxide is a toxic, invisible gas from incomplete combustion
Carbon monoxide (CO) is a colourless, odourless, and toxic gas that is formed when carbon-containing compounds undergo incomplete combustion. This process occurs when there is an insufficient amount of air (oxygen) to facilitate the complete burning of the compound, resulting in the formation of carbon monoxide instead of carbon dioxide (CO2).
In the context of cars, carbon monoxide is produced as a by-product of the combustion process in the engine. While individual cars produce relatively small amounts of emissions, the large number of vehicles on the road contributes significantly to air pollution. Carbon monoxide emissions from cars are particularly concerning due to their invisible and odourless nature, making it difficult for people to detect and avoid exposure.
Carbon monoxide is considered highly toxic to humans. When inhaled, carbon monoxide molecules displace oxygen in the body, leading to poisoning. The symptoms of carbon monoxide poisoning are often flu-like, making it challenging for individuals to recognise the early signs of exposure. As a result, victims may ignore the initial warnings, eventually leading to loss of consciousness and, in severe cases, death. According to the CDC, approximately 400 people in the United States die from unintentional carbon monoxide exposure each year.
Carbon monoxide is not only a concern for car emissions but also for various other sources. These include the combustion of fuels such as wood, coal, charcoal, oil, paraffin, propane, and natural gas. Additionally, indoor sources of carbon monoxide can include malfunctioning fuel-burning stoves, heaters, and blocked flues. Tobacco smoke is another source of carbon monoxide, particularly in low- and middle-income countries.
To mitigate the risks associated with carbon monoxide exposure, several preventative measures can be taken. These include installing CO alarms, maintaining fuel-burning appliances, and ensuring proper ventilation in enclosed spaces. Additionally, when using fuel-burning devices, it is essential to follow safety guidelines, such as avoiding the use of outdoor appliances indoors and refraining from running vehicles in attached garages.
In summary, carbon monoxide is a toxic, invisible gas produced by the incomplete combustion of carbon-containing compounds, including the combustion processes in car engines. Its presence in the atmosphere, particularly in urban areas, poses a significant health risk to humans, requiring proactive measures to prevent exposure and poisoning.
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Nitrogen oxides are reddish-brown gases that irritate the lungs
Nitrogen oxides (NOx) are a group of highly reactive gases that are reddish-brown in colour and can irritate the lungs. They are formed by the burning of fossil fuels such as coal, oil, methane gas (natural gas) or diesel at high temperatures. NOx is composed of nitrogen and oxygen, with nitrogen dioxide (NO2) and nitric oxide (NO) being the two most prevalent types. NO2 is a pungent gas with a brownish-red colour and a pungent smell. It is a major air pollutant and is harmful to human health, particularly the respiratory system.
Nitrogen oxides are released into the atmosphere through the combustion of fossil fuels in car engines, as well as from industrial processes such as oil and gas production, and coal-fired power plants. Cars, trucks, and buses are the largest sources of NO2 emissions. When NO2 is released into the atmosphere, it can undergo photochemical reactions with other air pollutants and sunlight, leading to the formation of ozone (O3) and other harmful substances.
The health effects of NO2 exposure are well-documented. Short-term exposure to high concentrations of NO2 can irritate the airways and aggravate respiratory diseases, especially asthma. It can lead to respiratory symptoms such as coughing, wheezing, and difficulty breathing, and may result in hospital admissions and visits to emergency rooms. Long-term exposure to elevated levels of NO2 is associated with more severe health consequences, including decreased lung function growth in children, intensified allergic responses, and an increased risk of premature death and cardiopulmonary effects.
Children are particularly vulnerable to the harmful effects of NO2 due to their higher breathing rate for their body weight and greater outdoor exposure duration. Studies have shown that prolonged NO2 exposure during childhood can lead to smaller lungs at maturity and an increased likelihood of developing asthma.
Regulators have recognised the importance of controlling NO2 emissions to reduce the overall impact of NOx on human health and the environment. Standards such as the Euro 7 emission standards aim to reduce NOx emissions from vehicles and set maximum limits on particulate emissions from brakes and tyres. Additionally, the federal Clean Air Act in the US has helped drive down nitrogen dioxide emissions and improve air quality nationwide.
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Sulfur dioxide is a colourless gas from burning crude oil
Cars are a major source of air pollution. The combustion process (exhaust) and the evaporation of fuel contribute to air pollution. Some of the chemicals that cars emit include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and hydrofluorocarbon (HFC) from leaking air conditioners. Carbon dioxide is a greenhouse gas and a major contributing factor to climate change.
In addition to the above, sulfur dioxide (SO2) is another air pollutant that cars release into the atmosphere. SO2 is a colorless gas or liquid with a strong, choking odor. It is produced from the burning of fossil fuels, such as coal and oil, and the smelting of mineral ores (aluminum, copper, zinc, lead, and iron) that contain sulfur.
When sulfur-containing fuels such as coal, petroleum oil, or diesel are burned, SO2 is formed. It can also change chemically into sulfate particles in the atmosphere, contributing to fine particle pollution. This type of pollution can be carried by the wind over long distances, affecting areas far from the source of emission.
The largest sources of SO2 emissions are power plants and other industrial facilities that burn fossil fuels. Smaller sources include locomotives, ships, and other vehicles and heavy equipment that burn high-sulfur fuel. Even electric vehicles with malfunctioning appliances or chimneys can release SO2 into the air.
Short-term exposure to high levels of SO2 can cause a burning sensation in the nose and throat, difficulty breathing, and aggravate existing heart disease. Long-term exposure can lead to changes in lung function and increased respiratory symptoms, especially during exercise or physical activity. Therefore, it is essential to take steps to reduce SO2 emissions and protect individuals from the harmful effects of this air pollutant.
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Hydrocarbons are unburnt fuel that escapes from exhausts
Cars are a major contributor to air pollution, particularly in towns and cities. The combustion of fuel in a car's engine produces exhaust gases, which are released into the atmosphere through the exhaust pipe. These gases often contain harmful chemicals, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).
Hydrocarbons are a key component of car fuel, and while they are meant to be fully burned during combustion, this process is never perfect. As a result, unburnt or partially burned hydrocarbons can escape from car exhausts. These unburnt hydrocarbons are one of the main causes of the unpleasant smell associated with car exhaust fumes.
When a car engine is started, the fuel does not always completely vaporize, leading to higher emissions of hydrocarbons and carbon monoxide. This issue diminishes as the engine reaches its operating temperature. Catalytic converters, which are designed to break down pollutants in exhaust gases, are also inefficient until they warm up to their operating temperature. Advances in technology, such as computer-controlled fuel injection and pre-heating of fuel, have helped reduce the duration of this start-up phase.
In addition to the combustion process, car fuel can also evaporate, contributing to air pollution. This is particularly an issue with gasoline, which is primarily composed of hydrocarbons. While ethanol blends have a lower carbon content than pure gasoline, they can still produce unburnt hydrocarbons in the exhaust, contributing to the overall pollution emitted by cars.
To reduce emissions, car manufacturers have introduced improvements in engine and exhaust system design, and catalytic converters and particulate filters are now standard on new petrol and diesel cars. Many cities have also implemented clean air zones to discourage the most polluting vehicles from entering congested areas.
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Frequently asked questions
Cars emit a range of harmful chemicals, including carbon dioxide (CO2), carbon monoxide (CO), nitrogen dioxide (NO2), methane (CH4), nitrous oxide (N2O) and hydrofluorocarbon (HFC) from leaking air conditioners.
Car emissions are believed to cause global warming, contributing to climate change. They are also believed to cause cancer and contribute to asthma, heart disease, birth defects and eye irritation.
While cars are a major contributor to air pollution, the production of electricity by coal-fired power plants can cause more pollution than most cars. Heating buildings with fuel other than electricity also pollutes the air.
