Helena Joyce
Vehicle exhaust emissions are a major contributor to air pollution in towns and cities, as well as global greenhouse gas emissions. The burning of fossil fuels such as natural gas, gasoline, diesel fuel, fuel oil, biodiesel blends, and coal results in the emission of exhaust gas, which is released into the atmosphere through an exhaust pipe or tailpipe. Pollutants from vehicle exhausts include benzene, carbon monoxide, nitrogen oxides, volatile organic compounds, particulate matter, and sulfur dioxide. These pollutants have been linked to adverse health effects, including allergies, skin irritation, heart disease, respiratory problems, and lung cancer.
| Characteristics | Values |
|---|---|
| Particulate matter (PM) | Soot, black carbon, volatile organic compounds (VOCs), hydrocarbons, nitrogen oxides, sulfur dioxides, benzene, acetaldehyde, 1,3-butadiene, formaldehyde |
| Nitrogen oxides (NOx) | Nitric acid vapour, nitrogen dioxide (NO2), nitrogen oxide (NO) |
| Volatile organic compounds (VOCs) | Benzene, acetaldehyde, 1,3-butadiene |
| Other gases | Carbon monoxide (CO), Sulfur dioxide (SO2), Carbon dioxide (CO2) |
| Other | Benzene (C6H6), a carcinogenic substance found in petrol and diesel |
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Carbon monoxide
The combustion process generates high amounts of carbon monoxide – over 30,000 parts per million (ppm) for the typical vehicle. To control exposure, cars are equipped with a catalytic converter, which combines oxygen with carbon monoxide to form carbon dioxide. Once the substance passes to the exhaust manifold, the amount of carbon monoxide is reduced to about 1,000 ppm. Without this process, a car can release 30,000 ppm or higher concentrations of carbon monoxide from the tailpipe.
A defective exhaust system can lead to carbon monoxide poisoning. Defects, including leaks from rusted components or a damaged catalytic converter, interrupt the process of reducing carbon monoxide emissions. As a result, you may be exposed to concerning amounts of carbon monoxide through the heating and cooling system or diverted directly into the cabin. Driving a vehicle with the trunk lid or rear tailgate open, or with holes in the car body, can also pull carbon monoxide from outside the vehicle and cause it to circulate through the interior.
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Nitrogen oxides
To mitigate the harmful effects of nitrogen oxides, various measures have been implemented. Car manufacturers have introduced improved engine and exhaust system designs, and catalytic converters and particulate filters are now standard on new petrol and diesel cars. Many cities worldwide have established clean air zones to discourage the most polluting vehicles from entering congested areas. Additionally, emission standards and regulations have become increasingly stringent over time to limit the release of harmful nitrogen oxide pollutants into the atmosphere.
It is worth noting that while efforts are being made to reduce nitrogen oxide emissions, diesel exhaust, in particular, remains a concern. Some countries have set deadlines to stop selling diesel vehicles, and certain city centers plan to implement bans on diesel cars in the future.
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Benzene
The use of unleaded gasoline and the increasing number of vehicles in Bangkok, for example, have significantly influenced benzene and toluene concentrations in vehicular emissions, contributing to air pollution. Older diesel vehicles, in particular, are known to produce harmful particulate emissions, and drivers of these vehicles are being discouraged from entering towns and cities with low emission zones.
While benzene exposure can occur after accidental spills or in industrial settings, the greater concern is low-level exposure over a protracted period. Studies have linked occupational exposure to benzene to leukaemia. However, the levels of benzene exposure in cars are significantly lower than the minimum occupational exposure linked to health issues.
To reduce exhaust emissions, car manufacturers have improved engine and exhaust system designs, and catalytic converters and particulate filters are now standard on all new petrol and diesel cars. Many cities have also introduced clean air zones to discourage the most polluting vehicles from entering.
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Particulate matter
Diesel exhaust is the primary component of traffic-related PM, contributing especially to the smaller, more harmful particles, PM2.5 and UFP. Older diesel vehicles, in particular, are known for their harmful particulate emissions, which include airborne particles of black soot and metal. These particles can invade the brain via the olfactory route or act through peripheral system responses, leading to inflammation and oxidative stress in the brain. Inhalation of diesel exhaust fumes has been linked to an increased risk of lung cancer, as well as other diseases such as asthma and heart disease.
Gasoline cars produce more carbonaceous particulate matter than modern diesel cars equipped with filters. Carbonaceous PM includes black carbon (BC), primary organic aerosol (POA), and secondary organic aerosol (SOA). SOA formation from gasoline cars far exceeds that of diesel cars, and laboratory experiments have shown that this is more pronounced at lower temperatures.
While vehicle emissions standards and clean air zones are helping to reduce particulate emissions, the vast number of petrol and diesel vehicles on the road, estimated at over 1.45 billion globally, continues to have a significant impact on air quality and public health.
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Sulphur dioxide
The presence of sulphur dioxide in vehicle emissions is a concern because of its impact on both human health and the environment. Short-term exposure to sulphur dioxide can harm the human respiratory system and make breathing difficult, especially for people with asthma, including children.
In the atmosphere, sulphur dioxide emissions can lead to the formation of other sulphur oxides (SOx) and particulate matter (PM) pollution. These particles are released into the airstream and can have damaging effects on human health. They can penetrate deeply into sensitive lung tissue and cause or worsen respiratory diseases such as emphysema and bronchitis, and even lead to premature death in extreme cases.
To mitigate the presence of sulphur dioxide in vehicle exhaust, catalytic converters are used. These devices take the sulphur dioxide out of the exhaust, reducing the amount released into the atmosphere. However, if there is a leak in the exhaust system, it is possible for sulphur dioxide to leak into the cabin of the vehicle, exposing the occupants to this harmful gas.
With growing concerns about environmental impact and population health, there is a renewed interest in finding cost-effective ways to improve air quality, such as through the use of alternative fuels like natural gas, which has a lower impact on global warming compared to traditional fuels.
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Frequently asked questions
The predominant sources of carbon monoxide (CO) in the air are motor vehicles. Other major pollutants found in vehicle exhaust are nitrogen oxides (NOx), particulate matter (PM), benzene, acetaldehyde, and 1,3-butadiene.
Pollutants from vehicle exhaust can affect more than just the lungs. They pose health risks at every stage of life and can even cause premature death. Exposure to these pollutants has been linked to adverse impacts on nearly every organ system in the body. Inhalation of NOx increases the risk of lung cancer and colorectal cancer. In addition, nitrogen oxides can irritate the respiratory system, causing coughing, choking, and reduced lung capacity.
Many cities around the world have introduced clean air zones to discourage the most polluting vehicles from entering. Car manufacturers are also reducing exhaust emissions through improved engine and exhaust system design, and catalytic converters and particulate filters are now standard on all new petrol and diesel cars.
