Vehicle Exhaust: Deadly Emissions And Their Impact

Vehicle exhaust is a major contributor to harmful pollution, with over 1.45 billion petrol and diesel vehicles on the road globally. These vehicles emit harmful gases and particulate matter, such as soot, nitric and sulfuric acids, nitrogen oxides, carbon monoxide, and volatile organic compounds, which have detrimental effects on human health and the environment. The combustion of fuels in internal combustion engines releases these pollutants, which disperse through exhaust pipes, contributing to air pollution and climate change. The health impacts of vehicle exhaust pollution range from respiratory issues, including asthma and lung cancer, to cardiovascular diseases and premature death. Additionally, the environmental consequences include the formation of ground-level ozone, a key component of smog, and the release of greenhouse gases, exacerbating climate change. While regulatory standards and technological advancements have helped reduce emissions, the complex nature of local air pollution from vehicles warrants further exploration of cost-effective solutions.

Particulate matter and soot

The particulate matter and soot in vehicle exhaust emissions are of great concern due to their detrimental impact on human health and the environment. Particulate matter refers to the collected matter on a flow-through filter, while "particle" denotes aerosol particles measured while airborne. These particles are a mix of solid and liquid components in the air, stemming from both natural and anthropogenic sources.

Diesel engines are notorious for emitting airborne particles of black soot and metal, known as diesel particulate matter (DPM) or diesel exhaust particles (DEP). DPM comprises diesel soot, ash particulates, metallic abrasion particles, sulfates, and silicates. These particles are primarily in the invisible sub-micrometer range, with a size of 100 nanometers, classifying them as ultrafine particles that can easily be inhaled. The inhalation of these fine particles can stimulate nerves in the lungs, leading to reflex coughing, wheezing, and shortness of breath. Additionally, the rough surfaces of these particles enable them to bind with other toxins in the environment, amplifying the hazards associated with their inhalation.

The health risks associated with particulate matter and soot in vehicle exhaust are significant. According to the World Health Organization, long-term exposure to diesel exhaust fumes is linked to an increased risk of lung cancer. Additionally, diesel exhaust is implicated in other diseases such as asthma, heart and lung damage, and adverse effects on mental function. The small particles in diesel exhaust can penetrate sensitive lung tissue, causing or exacerbating respiratory diseases such as emphysema and bronchitis.

The combustion of fuels, including gasoline, diesel, and natural gas, in internal combustion engines, is the primary source of exhaust gases and the associated particulate matter and soot. The largest components of most combustion gases are nitrogen (N2), water vapour (H2O), and carbon dioxide (CO2). However, the combustion process also releases harmful pollutants, including carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). These pollutants have been linked to various health issues, including respiratory problems, allergies, skin irritation, and heart disease.

To mitigate the harmful effects of particulate matter and soot in vehicle exhaust, several measures have been implemented. Modern cars are now equipped with diesel particulate filters (DPFs) to reduce the emission of harmful particles. Additionally, catalytic converters have been mandated in vehicles to break down exhaust gas pollutants using catalysts. These converters contain precious metals that neutralise local pollutants, converting them into harmless gases. The implementation of exhaust standards and the establishment of clean air zones in cities have also played a crucial role in reducing particulate matter and soot emissions from vehicles.

Health risks and premature death

Vehicle exhaust emissions are a major source of outdoor air pollution worldwide. The health impacts of vehicle exhaust are immense but unevenly distributed, both geographically and among various segments of the transportation sector.

A study by the International Council on Clean Transportation (ICCT) found that vehicle tailpipe emissions were linked to approximately 361,000 premature deaths from ambient particulate matter (PM2.5) and ground-level ozone worldwide in 2010, and 385,000 in 2015. Of these, 60,000 were attributed to emissions from shipping. On-road diesel vehicles were responsible for nearly half of the health impacts of air pollution from vehicles worldwide in 2015, and two-thirds of impacts in India, France, Germany, and Italy.

The Global Burden of Disease (GBD) study in 2017 reported that ambient air pollution contributed to 3.4 million premature deaths annually from heart and lung diseases and diabetes. The study also found that the number of transportation-attributable deaths per 100,000 population in London and Paris was approximately 2 to 3 times higher than the global average.

Vehicle exhaust emissions contain harmful pollutants such as nitrogen oxides (NOx), carbon monoxide (CO), and particulate matter (PM). These pollutants can have serious health impacts, including respiratory problems, allergies, skin irritation, and heart disease. Long-term exposure to diesel exhaust fumes has also been linked to an increased risk of lung cancer, according to the World Health Organization. Inhalation of NOx species further increases the risk of lung and colorectal cancer and can cause or worsen respiratory diseases such as emphysema and bronchitis.

Additionally, a blockage in a vehicle's exhaust system can lead to carbon monoxide poisoning. Breathing in high levels of carbon monoxide can cause headaches, respiratory problems, and even death.

The health risks and premature deaths associated with vehicle exhaust emissions highlight the importance of implementing measures to reduce air pollution from the transportation sector. This includes improving engine and exhaust system design, using catalytic converters and particulate filters, and establishing clean air zones to discourage polluting vehicles from entering densely populated areas.

Climate change and global emissions

Climate change is a pressing issue, and vehicle emissions are a significant contributor. Transportation is one of the largest sources of global warming emissions, particularly in the US, where the transportation sector produces nearly 30% of all global warming emissions. Cars and trucks alone account for nearly one-fifth of US emissions, emitting around 24 pounds of carbon dioxide and other global warming gases for every gallon of gas. The bulk of these emissions, around 19 pounds per gallon, come directly from a car's tailpipe, with the remaining 5 pounds coming from the extraction, production, and delivery of the fuel.

Highway vehicles release about 1.5 billion metric tons of greenhouse gases into the atmosphere annually, with carbon dioxide (CO2) being the primary constituent. Each gallon of gasoline burned creates approximately 20 pounds of greenhouse gases, translating to 5 to 9 tons of greenhouse gases yearly for an average vehicle. The combustion of gasoline results in the separation of carbon and hydrogen atoms, with hydrogen combining with oxygen to form water, and carbon uniting with oxygen to produce carbon dioxide.

To address this issue, the US Environmental Protection Agency (EPA) has implemented several initiatives. For instance, the SmartWay light-duty program identifies the most fuel-efficient and environmentally friendly vehicles to guide consumers' purchases. Additionally, the EPA and the Department of Transportation (DOT) have established regulations for greenhouse gas emissions and fuel economy standards for cars, light trucks, and heavy-duty trucks. These regulations are expected to significantly reduce greenhouse gas emissions and improve fuel efficiency, with projected savings for consumers and a reduction in America's dependence on foreign oil.

Furthermore, the 2007 Energy Independence and Security Act mandates that federal agencies acquire low-emission vehicles, such as electric cars, light trucks, or medium-duty passenger vehicles. The EPA annually evaluates the greenhouse gas emissions performance of federal fleets, encouraging the purchase of high-performing, environmentally friendly vehicles. The Renewable Fuel Standard program, created by Congress, also aims to reduce greenhouse gas emissions by promoting the use of renewable fuels derived from plants, crops, and biomass, which have a lower environmental impact than fossil fuels.

It's important to note that individual choices, such as the type of car purchased and driving habits, can significantly impact an individual's contribution to climate change. Cleaner vehicles and technologies, along with strategies to reduce vehicle miles traveled, can help mitigate the environmental impact of the transportation sector.

Local air pollution and clean air zones

Motor vehicles are a significant source of air pollution, with transportation accounting for about half of emissions in cities. Vehicle exhaust emissions contain harmful gases and particles, such as carbon monoxide, nitrogen oxides, and particulate matter, which can have detrimental effects on human health and the environment.

To mitigate this issue, many cities worldwide have introduced Clean Air Zones (CAZs) or similar schemes like Low Emission Zones and Zero Emission Zones. CAZs are areas where measures are implemented to discourage the most polluting vehicles from entering, with the aim of improving air quality and reducing harmful emissions. These zones can have a positive impact on public health, particularly for vulnerable groups, by reducing exposure to harmful pollutants and improving respiratory health. The improved air quality that results from CAZs can also lead to increased workforce productivity, safer streets, and contributions to a city's net-zero goals and sustainable urbanization.

One successful example of a CAZ is London's Ultra Low Emission Zone (ULEZ), which was introduced in 2019 and covers a large area of central London. The ULEZ applies a daily charge to vehicles that do not meet specific emission standards, and it has significantly reduced air pollution, especially nitrogen dioxide levels. This has resulted in improved air quality and health benefits for Londoners. Other cities that have implemented CAZs or similar initiatives include Bath, Brighton, Portsmouth, and Krakow, with many more developing plans to address air pollution through well-planned transport systems, walkable streets, and green spaces.

While CAZs offer numerous advantages, there are also challenges to consider. Ensuring compliance with regulations and charges within CAZs can be complex, and effective enforcement mechanisms are essential for the success of these initiatives. Additionally, addressing social equity concerns and providing support for the transition to cleaner vehicles are crucial aspects of implementing CAZs. Accurate data collection and monitoring are vital to assess the effectiveness of these zones in reducing air pollution.

Overall, CAZs and similar schemes play a crucial role in reducing local air pollution caused by vehicle exhaust emissions, improving public health, and contributing to sustainable urban development.

Catalytic converters and exhaust standards

The core purpose of catalytic converters in automotive systems is to reduce the emission of harmful pollutants from an engine's exhaust gases and make them more environmentally friendly. They are usually used with internal combustion engines fuelled by gasoline or diesel. The first widespread introduction of catalytic converters was in the United States automobile market in 1975 to comply with the US Environmental Protection Agency's stricter regulation of exhaust emissions. These "two-way" converters combined oxygen with carbon monoxide and unburned hydrocarbons to produce carbon dioxide and water.

Since 1993, car manufacturers have had to comply with a series of European emissions standards that set maximum limits for harmful substances emitted by new cars. Catalytic converters and particulate filters are now standard on all new petrol and diesel cars. The Euro 1 emission standards made catalytic converters mandatory on all new gasoline cars sold in the European Union and the United Kingdom from January 1, 1993.

The basic approach of catalytic converters has changed little since the 1970s: thin layers of precious metals inside the catalytic converter convert pollution into harmless gases. The precious metal palladium abates carbon monoxide and hydrocarbons, rhodium abates nitrogen oxides, and platinum abates all three. These reactions can eliminate essentially all pollution, but only under high temperatures and the right mix of air and fuel in the engine.

Local air pollution emissions from vehicles account for 40% of total US emissions and are associated with more than 37,000 deaths in the US and more than 250,000 deaths globally each year. However, over the past 50 years, emissions of hydrocarbons, nitrogen oxides, and carbon monoxide from vehicles have seen an impressive larger-than-99% reduction. This decrease has been caused by the implementation of exhaust standards, with other policies likely playing a negligible role.

Frequently asked questions