Car Exhaust: Poisoning Our Air And Health

Cars have transformed personal mobility across the world, but this has come at a cost: harmful air pollution. The vast number of petrol and diesel vehicles on the road—estimated at over 1.45 billion globally—has had a significant impact on the environment. Car exhaust emissions increase the levels of carbon dioxide and other greenhouse gases in the atmosphere, contributing to global warming and climate change. These emissions contain harmful substances, including nitrogen dioxide, benzene, and particulate matter, which can have serious effects on human health, from allergies and skin irritation to heart disease, respiratory problems, and even cancer. While advancements in technology and policy changes have helped reduce emissions in recent years, transportation remains a major source of air pollution, with exhaust fumes from cars being a key contributor.

Car exhausts emit harmful gases like carbon dioxide, nitrogen dioxide, and hydrocarbons

Car exhausts are a major source of air pollution, releasing harmful gases and particles that have detrimental effects on both the environment and human health. Among these emissions are carbon dioxide, nitrogen dioxide, and hydrocarbons, which contribute to global warming, air pollution, and health issues.

Carbon dioxide (CO2) is a greenhouse gas that is released into the atmosphere when cars burn fuel. While carbon dioxide is naturally present in the atmosphere and helps to keep some of the sun's heat, human activities, such as burning fossil fuels, have led to increased levels of this gas. This, in turn, contributes to global warming and climate change. The amount of carbon dioxide emitted is directly related to fuel consumption—as fuel consumption increases, so do carbon dioxide emissions.

Nitrogen dioxide (NO2) is another harmful gas released from car exhausts. It is formed when fuel burns and nitrogen and oxygen react to form nitrogen oxides (NOx). Breathing air with high concentrations of nitrogen dioxide can impact the respiratory system, causing coughing, choking, and reduced lung capacity. Additionally, when hydrocarbons and nitrogen oxides combine in the presence of sunlight, they produce ground-level ozone, which is a primary component of smog and contributes to respiratory problems.

Hydrocarbons, unburnt or partially burnt fuel, are also emitted from car exhausts. These volatile organic compounds (VOCs) react with nitrogen oxides in the atmosphere, forming ground-level ozone. Hydrocarbons include toxic pollutants such as benzene, acetaldehyde, and 1,3-butadiene, which have been linked to various types of cancer.

While advancements in technology and policies addressing climate change have helped reduce emissions, car exhausts continue to be a significant source of air pollution. The vast number of vehicles on the road, particularly in urban areas, contributes to the pollution experienced by people living in or near cities. Additionally, older vehicles, especially diesel engines, are major contributors to particulate matter pollution, releasing fine particles of soot, black soot, and metal into the air.

Particulate matter, like soot and metal particles, is released from car exhausts

The combustion engines of cars emit harmful pollutants into the air. Among these emissions is particulate matter, which includes soot and metal particles.

Particulate matter is a mixture of solid particles and liquid droplets found in the air that contribute to atmospheric haze. These particles can damage the lungs and enter the bloodstream. They can also reduce visibility and adversely affect climate, ecosystems, and materials. Fine particulate matter, or particles that are 2.5 microns or less in diameter (PM2.5), are associated with the greatest proportion of adverse health effects related to air pollution. Short-term exposure to PM2.5 has been linked to worsening respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD), often resulting in hospitalisation. Long-term exposure to PM2.5 has been linked to premature death, particularly in people with chronic heart or lung diseases, and reduced lung function growth in children.

Soot, a component of particulate matter, is composed largely of carbon-based particles resulting from the incomplete burning of hydrocarbons or organic fuel. It is released from the combustion engines of cars, particularly diesel engines. Soot tends to settle on surfaces but can also decompose while still airborne. It is a major contributor to hazardous air pollution, accounting for over one-quarter of the total. Long-term exposure to soot in urban air pollution has been linked to an increased risk of coronary artery disease.

Metal particles are also released from car exhausts as particulate matter. These particles can include metallic compounds, as well as inorganic ions, elemental carbon, organic compounds, and compounds from the earth's crust. Modern cars are fitted with diesel particulate filters (DPFs) to reduce the number of harmful particles being released into the atmosphere. However, reports from the Air Quality Expert Group indicate that even electric cars will still contribute to air pollution from brake and tyre wear.

Brakes and tyres also contribute to harmful car emissions

Cars are a major contributor to air pollution. While exhaust fumes are a significant source of harmful emissions, brakes and tyres also contribute to the problem. Every time a car is driven, tiny fragments of particulate matter are released from the wear and tear of brakes and tyres, as well as from the road surface. These particles, including dust, enter the airstream and can have detrimental effects on human health and the environment.

Brake wear is a significant source of particulate matter, with studies indicating that it contributes to traffic-related PM emissions. The particles released from brakes are characterised by high concentrations of metals such as iron (Fe) and copper (Cu), which can lead to oxidative stress in biological tissues. Transition metals, such as Fe, Cu, nickel (Ni), and chromium (Cr), are of particular concern due to their ability to produce reactive oxygen species (ROS). Additionally, metals like zinc (Zn), aluminium (Al), and lead (Pb) can influence the toxic effects of transition metals, either enhancing or reducing their activity.

Tyre wear is another significant contributor to harmful emissions. Tests have shown that tyre wear produces almost 2,000 times more particle pollution than exhaust emissions in modern cars. These particles, including toxic organic compounds and known carcinogens, pollute the air, water, and soil. The increasing weight of cars further exacerbates the issue, as heavier vehicles throw off more particles from tyre wear. Tyre particles can also contain plastic, which can harm marine wildlife if deposited in water through sewers.

The issue of brake and tyre emissions is not limited to traditional petrol and diesel vehicles. Electric vehicles (EVs) have also been found to produce particulate matter pollution from brake and tyre wear. However, it is important to note that EVs generally have longer brake lifespans than their petrol and diesel counterparts, resulting in reduced particulate matter emissions.

To address the issue of brake and tyre emissions, upcoming Euro 7 emission standards will include officially measured brake and tyre emission limits. Additionally, while there are currently limited regulations on tyre wear rates and the chemicals they contain, analysts suggest that even small changes can have a significant impact on reducing their environmental footprint.

Car exhaust pollution disproportionately affects low-income communities and communities of colour

Car exhaust emissions have transformed personal mobility across the world, but they have also contributed to harmful pollution. With over 1.45 billion petrol and diesel vehicles on the road globally, vehicles are a major contributor to air pollution in towns and cities, as well as global greenhouse gas emissions.

While vehicle emissions have decreased over time due to improved engine and exhaust system design, catalytic converters, and particulate filters, certain communities are still disproportionately affected by car exhaust pollution. Non-white and low-income communities are more likely to be exposed to hazardous air pollution ingredients, such as vanadium, nitrates, and zinc, which are linked to hospitalizations or deaths from cardiovascular and lung disease.

A study by Miranda and colleagues found that African Americans are more likely to live in areas with higher levels of particulates and ozone, the main ingredients of smog. Similarly, Hispanics and low-income residents are overrepresented in counties with high fine particle pollution. Research by UC Berkeley's Morello-Frosch and Bill Jesdale also revealed that cancer risks from air toxics, such as benzene and formaldehyde, are greatest in highly segregated metropolitan areas, with the risks increasing with the degree of segregation across all racial and ethnic groups, but especially for Hispanics.

Furthermore, communities of colour and low-income communities are often located near busy roads, refineries, or power plants, increasing their exposure to vehicle exhaust pollutants. For example, Boyle Heights in East Los Angeles, a predominantly Hispanic and low-income community, experiences high levels of vehicle exhaust emissions due to its proximity to major roadways.

To address these disparities, policies such as clean air zones and emission standards have been implemented to discourage polluting vehicles from entering certain areas and reduce vehicle tailpipe emissions. However, these policies may not always target older, high-emitting vehicles, and can inadvertently increase the demand for older, dirtier vehicles among consumers. As a result, there is a growing interest in electric vehicles and calls for stronger emission standards to improve air quality and protect the health of all communities.

Fuel composition and engine design influence the amount of exhaust emission

Exhaust emissions refer to the particles and gases released by vehicles, which are a major source of air pollutants that negatively impact human health. These emissions can be reduced by controlling fuel composition and vehicle engine design.

Fuel composition has been controlled to restrict the amounts of lead, sulfur, and aromatic compounds in the fuel and to reduce its volatility. For example, the use of fuels with alcohol additives, and unleaded gasoline helps minimize pollutants from the combustion chamber. Additionally, the formulation of gasoline, air-fuel ratio, ignition timing, and compression ratio all influence the amount of exhaust emission produced by gasoline-powered vehicles.

Improvements in engine design, such as the introduction of three-way and two-way catalytic converters, have significantly reduced the levels of pollutants produced by vehicles. These catalytic converters work by breaking down the pollution of exhaust gases using a catalyst. However, they may also produce unwanted by-products such as hydrogen sulfide and ammonia. Advances in technology, such as computer-controlled fuel injection, shorter intake lengths, and pre-heating of fuel, have also helped to reduce emissions.

The layout and design features of exhaust systems are crucial, as the gaseous emissions from internal combustion engines can be toxic to human life. Poor design or careless use of these systems has led to accidents, some of which have been fatal. To optimize efficiency and emissions, engine structural strength and performance/emissions calibration must be considered.

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