Vehicle Emissions: Air Pollution's Unseen Culprit

Vehicles are a major source of air pollution, with transportation being a significant contributor to climate change in the United States. Cars, trucks, and buses produce a significant amount of harmful emissions, including carbon monoxide, nitrogen oxides, and hydrocarbons. These emissions can lead to serious health issues, such as respiratory problems and even premature death. Additionally, the burning of gasoline and diesel fuel releases carbon dioxide, the primary greenhouse gas, contributing to global warming. While individual car emissions may seem small, the large number of vehicles on the road results in substantial air pollution, particularly in urban areas. To reduce vehicle pollution, individuals can choose more fuel-efficient vehicles, carpool, and maintain their vehicles, while governments can implement emission control programs and support the adoption of zero or low-emission vehicles.

Vehicle emissions

Carbon monoxide is a colorless and odorless gas that can be deadly. It forms when fuel does not burn completely and combines with blood, limiting its ability to transport oxygen. Nitrogen oxides, including nitrogen oxide (NO) and nitrogen dioxide (NO2), are formed when nitrogen in the air reacts with oxygen during fuel combustion. These gases irritate the lungs and eyes and contribute to smog and acid rain. Hydrocarbons, another vehicle emission, react with nitrogen oxides in the presence of sunlight to form ground-level ozone, a primary component of smog.

Particulate matter, or soot, from vehicle exhaust, is composed of fine particles that can penetrate deep into the lungs and cause serious health issues. Volatile Organic Compounds (VOCs), such as benzene, acetaldehyde, and 1,3-butadiene, are toxic air pollutants linked to cancer. Additionally, sulfur dioxide (SO2) is produced by burning sulfur-containing fuels, particularly diesel, and can react in the atmosphere to form fine particles, posing health risks, especially to children and asthmatics.

To reduce vehicle emissions and mitigate their impact on air pollution, several strategies can be employed. These include driving less, carpooling, using public transportation, and choosing fuel-efficient or electric vehicles. Proper vehicle maintenance, such as regular oil changes and keeping the engine in good repair, can also help reduce emissions. Additionally, governments and organizations play a crucial role in implementing policies and programs to support the adoption of zero- and low-emission vehicles, promoting cleaner fuels, and enforcing emission control regulations.

Individual driving habits can also make a difference. Observing speed limits, accelerating gradually, and avoiding excessive idling can reduce fuel consumption and emissions. Choosing less congested routes and maintaining a safe distance from other vehicles can further lower traffic-related emissions. While inside a vehicle, keeping windows closed and recirculating cabin air during heavy traffic or stoplights can reduce exposure to outdoor air pollutants.

Gasoline and diesel fuel

Gasoline, a highly toxic and flammable liquid, releases vapors and substances during combustion that contribute to air pollution. The combustion of gasoline produces carbon monoxide, nitrogen oxides, particulate matter, unburned hydrocarbons, and carbon dioxide, a significant greenhouse gas. In 2022, combustion-related CO2 emissions from aviation and motor gasoline in the US were about 22% of total energy-related CO2 emissions. Additionally, the presence of lead in gasoline posed health concerns, leading to the installation of catalytic converters in new vehicles from 1976 to reduce toxic air pollutant emissions.

Diesel engines, on the other hand, operate with excess air, resulting in very low but still measurable carbon monoxide emissions. However, the combustion process can transform nitrogen from the air into nitrogen oxides, which are reddish-brown gases that irritate the lungs and eyes. Diesel exhaust is a major contributor to particulate matter (PM) pollution, which includes fine particles that pose serious health threats. Diesel engines also emit volatile organic compounds (VOCs) that react with nitrogen oxides to form ground-level ozone, a primary component of smog.

The transportation sector, including gasoline and diesel-powered vehicles, is a major source of air pollution and climate change. In the United States, tailpipe emissions from cars, trucks, and buses account for over one-fifth of the country's total global warming pollution. The different fuel types used in vehicles cause spatial variability in short-lived climate forcers (SLCFs) emissions, impacting surface air quality and pollution levels.

To mitigate the environmental and health impacts of gasoline and diesel fuel vehicles, several measures have been implemented. These include the adoption of cleaner-burning reformulated gasoline, the phase-out of leaded gasoline, and the development of ultra-low sulfur gasoline to reduce emissions from old and new vehicles. Additionally, the creation of emission standards, the implementation of inspection and maintenance programs, and the promotion of electric, hybrid, and fuel-efficient vehicles aim to reduce pollution from gasoline and diesel fuel transportation.

Carbon dioxide and carbon monoxide

Carbon dioxide (CO2) and carbon monoxide (CO) are two of the most common byproducts of burning gasoline and diesel fuel. They are also two of the most harmful, contributing significantly to air pollution and climate change.

Carbon dioxide is a greenhouse gas, and it is the most common human-caused greenhouse gas. The average passenger vehicle emits about 400 grams of CO2 per mile, with a typical passenger car emitting around 4.6 metric tons of CO2 per year. This assumes an average fuel economy of 22.2 miles per gallon and an annual mileage of 11,500 miles. Burning one gallon of gasoline produces approximately 8,887 grams of CO2, while burning a gallon of diesel produces 10,180 grams. Most of the weight of the CO2 comes from the oxygen in the air, not the fuel itself.

In addition to carbon dioxide, vehicles emit methane (CH4) and nitrous oxide (N2O) from the tailpipe, and all vehicles can emit hydrofluorocarbon (HFC) from leaking air conditioners. While electric vehicles (EVs) do not have tailpipe emissions, emissions are still created during the production and distribution of the electricity used to power them.

Carbon monoxide is a highly toxic, colorless, and odorless gas. It is produced through the incomplete burning of fuels such as propane, coal, wood, oil, kerosene, natural gas, and gasoline. The internal combustion engine, a primary component of gasoline-fueled automobiles, is one of the most common sources of CO exposure. While changes in engine design, fuel, and emission control devices have reduced CO emissions, faulty or poorly maintained exhaust systems can result in increased CO levels within the vehicle cabin.

The lethal consequences of carbon monoxide exposure are well-documented, with hundreds of people dying each year from CO poisoning caused by a running vehicle, often in an enclosed space like a garage. Carbon monoxide combines with blood and limits its ability to transport oxygen, which can quickly lead to death or serious illness. Operating a vehicle with a defective exhaust or emission system, driving with the trunk lid or tailgate open, or with holes in the body, can all increase the risk of CO exposure.

To reduce emissions of both CO2 and CO, individuals can opt for more fuel-efficient vehicles, including electric or hybrid models, and drive less, choosing to walk or bike to their destination when possible. Maintaining vehicles and keeping them in good repair is also important, as newer vehicles have complex emission controls to keep them running as cleanly as possible.

Nitrogen oxides and hydrocarbons

Hydrocarbons, on the other hand, are emitted from vehicles as a result of incomplete fuel combustion. These hydrocarbons react with nitrogen oxides in the presence of sunlight to form ground-level ozone, a major component of smog. This ground-level ozone irritates the respiratory system and poses serious health risks, particularly to children, the elderly, and people with lung diseases such as asthma.

To combat NOx emissions, several technologies have been developed. One common method is the use of three-way catalytic converters, which are effective in reducing NOx emissions in gasoline engines. These converters simultaneously control carbon monoxide, unburned hydrocarbons, and NOx, converting them into less harmful substances like nitrogen, water, and carbon dioxide. Diesel engines, however, present a greater challenge due to their higher oxygen intake, which makes the necessary chemical reaction for NOx reduction more difficult.

Aftertreatment methods, such as Lean NOx Traps (LNT) and Selective Catalytic Reduction (SCR), are also employed to reduce NOx emissions in diesel vehicles. LNTs use catalysts to temporarily store NOx, while SCR uses ammonia as a reductant to reduce NOx over a catalyst. Additionally, exhaust gas recirculation (EGR) techniques address NOx formation inside the engine cylinder.

Reducing vehicle emissions can be achieved through a combination of regulatory measures, technological advancements, and individual choices. Regulatory efforts, such as the federal Clean Air Act of 1990, aim to control vehicle emissions and promote cleaner technologies. At the same time, technological advancements have led to the development of zero-emission vehicles (ZEVs) and more fuel-efficient models, helping to reduce both NOx and hydrocarbon emissions.

Individuals can also play a significant role in reducing air pollution from vehicles. Choosing to drive fuel-efficient or electric vehicles, maintaining proper vehicle maintenance, and adopting driving practices that reduce fuel consumption, such as observing speed limits and accelerating gradually, can collectively contribute to lower emissions and improved air quality.

Health risks and environmental impact

The health risks and environmental impact of air pollution from vehicles are significant and wide-ranging. Vehicle emissions contribute to both air pollution and carbon dioxide pollution, the latter being the principal greenhouse gas. While carbon dioxide is not harmful in itself, burning gasoline and other fossil fuels releases far more carbon dioxide than the planet can handle, leading to a heat-trapping layer in the atmosphere that contributes to global warming and climate change.

In the US, vehicle emissions are the largest source of carbon monoxide, with 56% nationwide and up to 95% in cities. Carbon monoxide is a dangerous, colorless, and odorless gas that combines with blood and limits its ability to transport oxygen. Additionally, vehicles are a major source of nitrogen oxides, which irritate the lungs and eyes and contribute to environmental issues such as acid rain, deteriorated water quality, and soil and surface water acidification. Diesel vehicles are a significant contributor, with 60% of nitrogen oxide emissions in US transportation coming from this source.

Furthermore, vehicles emit harmful pollutants such as volatile organic compounds (VOCs), particulate matter, benzene, acetaldehyde, and 1,3-butadiene. These pollutants are linked to respiratory issues, coughing, choking, and reduced lung capacity, and even different types of cancer. Fine particles, less than one-tenth of the diameter of a human hair, can penetrate deep into the lungs and pose serious health risks, especially to young children and asthmatics.

The impact of vehicle pollution on human health is severe, with 17,000 to 20,000 people dying annually in the US from vehicle pollution. People of color are disproportionately affected, breathing more air pollution from cars and trucks in some regions. Additionally, those inside vehicles are exposed to higher levels of harmful pollutants than those outside due to the cabin acting as a confined space. California, in particular, has consistently ranked among the states with the worst air quality, with nine out of ten Californians living in areas with unhealthy air.

To mitigate these health and environmental risks, various measures can be taken. These include adopting zero or low-emission vehicles, such as electric, hybrid, or fuel-efficient options, and supporting their manufacture and sale. Additionally, maintaining vehicles and keeping them in good repair can help ensure they run as cleanly and efficiently as possible. Driving habits can also make a difference, such as observing speed limits, accelerating gradually, reducing mileage, and choosing less congested routes.

Frequently asked questions