Bronte Wells
Vehicles are a major contributor to air pollution, with emissions being the largest source of carbon monoxide and nitrogen oxides. The burning of gasoline and diesel fuel creates harmful byproducts such as nitrogen dioxide, carbon monoxide, hydrocarbons, benzene, and formaldehyde. These emissions contribute to global warming as greenhouse gases heat the planet and deplete the ozone layer, causing a rise in average global temperatures, sea levels, and an increase in natural disasters. While newer vehicles emit less pollution, the growing popularity of gas-guzzling SUVs and an increase in the number of cars on the road offset these improvements.
| Characteristics | Values |
|---|---|
| Global transport emissions in 2018 | Road travel accounted for three-quarters of transport emissions |
| Transport emissions sources | Passenger vehicles (cars and buses) contributed 45.1%, trucks carrying freight contributed 29.4%aviation contributed 11.6%</co: 0%, international shipping contributed 10.6%rail travel and freight contributed 1%</co: 0> |
| Total emissions from transport sector | 21% |
| Total emissions from road transport | 15% |
| US vehicle emissions | Largest source of carbon monoxides (56% nationwide and up to 95% in cities) and nitrogen oxides (45%) |
| California's transport sector emissions | 80% of nitrogen oxide pollution and 80% of pollutants that cause smog |
| Diesel vehicles' contribution to US transport sector NOx emissions | 60% |
| US GHG emissions from transport sector | 28% |
| Projected GHG reduction from light-duty GHG regulations for passenger vehicles and trucks in model years 2027-2032 | 7 billion metric tons |
| US fuel consumption reduction target | 20% by 2026 |
| US fuel consumption reduction | 5% as of 2015 |
| US fuel economy improvement since the mid-1970s | 4% |
| US renewable fuel production in 2014 | 14.3 billion gallons |
| US renewable fuel production target for 2015 | 15 billion gallons |
| Global temperature rise correlation | Up to 2024, the oceans absorbed 90% of the extra heat caused by carbon dioxide pollution, leading to a rise in ocean temperatures |
| Carbon dioxide emissions from gasoline | 20 pounds of carbon dioxide per gallon |
| US car emissions compared to 1960s | 98-99% cleaner for most tailpipe pollutants |
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What You'll Learn
Vehicle emissions: carbon dioxide and air pollution
Vehicle emissions are a significant contributor to air pollution and carbon dioxide pollution. Transportation is responsible for about 28% of total US greenhouse gas emissions, making it the largest contributor to US GHG emissions. Between 1990 and 2022, GHG emissions in the transportation sector increased more than any other sector.
A typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year. This number varies based on the vehicle's fuel, fuel economy, and the number of miles driven per year. Every gallon of gasoline burned creates about 8,887 grams of CO2, and the average vehicle emits about 400 grams of CO2 per mile. Modern vehicles are more fuel-efficient, which helps lower CO2 emissions per mile. However, the growing popularity of less fuel-efficient SUVs and pickup trucks, combined with Americans driving more miles, means the amount of gasoline burned has not decreased.
In addition to carbon dioxide, vehicles emit other greenhouse gases and air pollutants. Gasoline vehicles produce methane and nitrous oxide from the tailpipe, and all vehicles with air conditioning can emit hydrofluorocarbon (HFC) from leaking air conditioners. These emissions have a higher global warming potential than CO2. Nitrogen oxides from vehicles cause environmental issues such as acid rain and contribute to health issues such as asthma and heart problems.
Electric vehicles (EVs) do not have tailpipe emissions, but they do produce emissions during the production and distribution of electricity. Plug-in hybrid electric vehicles (PHEVs) that use both electricity and gasoline as fuel sources may also produce tailpipe emissions when operating on gasoline.
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Gasoline and diesel vehicles: harmful byproducts
Greenhouse gas emissions from transportation account for about 28% of total US greenhouse gas emissions, making transportation the largest contributor of US GHG emissions. A typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year. This number varies based on the vehicle's fuel, fuel economy, and the number of miles driven per year. Every gallon of gasoline burned creates about 8,887 grams of CO2, or about 20 pounds of CO2. Modern vehicles are more fuel-efficient, but the growing popularity of SUVs and pickup trucks offsets much of the progress made in fuel efficiency.
Gasoline vehicles produce methane (CH4) and nitrous oxide (N2O) from the tailpipe, and all vehicles with air conditioners can emit hydrofluorocarbon (HFC) from leaking air conditioners. While HFC emissions from gasoline vehicles are small compared to CO2, they have a higher global warming potential.
Diesel vehicles contribute 60% of NOx emissions in US transportation. NOx causes environmental issues such as acid rain, deteriorated water quality, and the acidification of soils and surface waters. It also forms ground-level ozone (smog) and PM2.5, both harmful to health and the environment. Nitrogen dioxide exposure can worsen asthma and cause serious health problems, including premature death, heart issues, impaired lung development, and breathing difficulties. Diesel particulate matter (DPM) is a complex mixture of gaseous and solid material, with more than 90% of DPM being less than 1 µm in diameter. DPM is mainly an urban problem, as most major sources of diesel emissions, such as ships, trains, and trucks, operate in and around highly populated areas. DPM plays an important role in climate change, as emissions of black carbon (BC) are the second largest contributor to global warming after carbon dioxide emissions.
While diesel engines manufactured today are cleaner than ever before, many older, dirtier engines are still in use. Diesel engines can operate for 30 years or more, and reducing exposure to diesel exhaust from these engines is important for human health and the environment.
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Electric vehicles: low emissions
Vehicles are a major contributor to air pollution. Every time a car is driven, pollution is emitted directly into the air, causing significant health risks, especially for those who live near busy roads. When gasoline is burned, carbon and hydrogen separate. The hydrogen combines with oxygen to form water, and carbon combines with oxygen to form carbon dioxide (CO2).
Electric vehicles (EVs) have a battery instead of a gasoline tank and an electric motor instead of an internal combustion engine. They do not emit any tailpipe emissions, although they do emit a small amount of greenhouse gases due to air conditioner leakage. EVs are responsible for considerably lower emissions over their lifetime than conventional (internal combustion engine) vehicles. In the UK in 2019, the lifetime emissions per kilometre of driving a Nissan Leaf EV were about three times lower than for the average conventional car.
However, it is important to note that the electricity used to power EVs is still largely produced from fossil fuels in many parts of the world, and the energy is used to manufacture the vehicle, particularly the battery. In countries with coal-intensive electricity generation, the benefits of EVs are smaller, and they can have similar lifetime emissions to the most efficient conventional vehicles. For example, a recent study in Germany found that "electric vehicles will barely help cut CO2 emissions over the coming years".
On the other hand, producing batteries in regions with relatively low-carbon electricity or in factories powered by renewable energy can substantially reduce battery emissions. In addition, as countries decarbonize electricity generation to meet their climate targets, driving emissions will fall for existing EVs and manufacturing emissions will fall for new EVs. For example, one study in Germany found that emissions from EVs are up to 43% lower than diesel vehicles.
Several cities have implemented low-emission zones to incentivize and accelerate the adoption of cleaner vehicles. Examples of zero-emission vehicles include muscle-powered vehicles such as bicycles, electric bicycles, and gravity racers, as well as battery electric vehicles and fuel cell vehicles powered by hydrogen.
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Fuel economy: reducing emissions
Vehicle emissions are a significant contributor to pollution, particularly in the form of carbon dioxide and air pollution. Carbon dioxide (CO2) is the primary greenhouse gas, and while it is not directly harmful and is necessary for life on Earth, burning gasoline and fossil fuels releases far more carbon dioxide than the planet can handle. This excess CO2 forms a heat-trapping layer in the atmosphere, contributing to climate change.
Transportation accounts for about 28% of total US greenhouse gas emissions, making it the largest contributor in the country. Within the transportation sector, passenger vehicles are a significant source of emissions, releasing about 4.6 metric tons of CO2 per year on average. This figure varies depending on the vehicle's fuel type, fuel economy, and annual mileage.
To address this issue, efforts have been made to improve fuel economy and reduce emissions. Modern vehicles are more fuel-efficient due to stricter fuel economy standards, which has helped lower CO2 emissions per mile. Additionally, the US Environmental Protection Agency (EPA) has implemented initiatives such as SmartWay, which helps the freight transportation sector improve supply chain efficiency, reduce greenhouse gases, and lower fuel costs. The EPA also provides resources like the Green Vehicle Guide to help consumers choose more fuel-efficient and environmentally friendly vehicles.
Furthermore, advancements in automotive and fuel technologies, intelligent transportation systems (ITS), and mobility management strategies offer significant potential for reducing emissions and fuel consumption. For example, electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) have lower or zero tailpipe emissions compared to traditional gasoline-powered vehicles. Renewable fuels produced from plants, crops, and biomass can also reduce greenhouse gas emissions compared to fossil fuels.
While progress has been made, there are still challenges to overcome. The increasing popularity of less fuel-efficient vehicles, such as SUVs and pickup trucks, and the rising number of vehicle miles traveled (VMT) have offset some of the gains made through improved fuel economy. Additionally, diesel vehicles contribute significantly to nitrogen oxide (NOx) emissions, which have adverse environmental and health impacts. Addressing these issues requires a combination of improved fuel economy, a shift towards low-carbon fuels, and strategies to reduce vehicle miles traveled, such as car-sharing and efficient mobility management systems.
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Vehicle miles travelled: impact on emissions
Vehicle miles travelled (VMT) is a metric that reflects the total distance travelled by cars and trucks during a given period. In the United States, VMT statistics from the US Federal Highway Administration begin in 1970, and since then, VMT-per-capita has grown significantly.
The impact of VMT on emissions is significant. As VMT from combustion engines increases, so do climate-forcing greenhouse gas (GHG) emissions due to increased tailpipe emissions. In 2021, the average carbon dioxide (CO2) emissions per mile for a new car were approximately 347 grams per mile, a decrease from 1975 where the average was almost 700 grams. This decrease in emissions per mile is due to improved vehicle efficiency and technological innovations. However, despite these improvements, the amount of gasoline burned has not decreased due to Americans driving more miles than ever, and the growing popularity of gas-guzzling SUVs and pickup trucks.
To address the impact of VMT on emissions, strategies such as reducing the number of vehicle miles travelled, improving vehicle technologies, and using low-carbon fuels can be implemented. For example, encouraging households to switch from single-occupant driving to carpooling, transit, biking, or walking can help reduce VMT and, consequently, emissions. Additionally, electric vehicles (EVs) emit significantly fewer GHGs than gasoline-powered vehicles, and plug-in hybrid electric vehicles (PHEVs) produce no tailpipe emissions when operating on electricity alone.
Furthermore, programs such as SmartWay by the EPA help improve supply chain efficiency in the freight transportation sector, reducing greenhouse gases and saving fuel costs. The Renewable Fuel Standard program also aims to reduce greenhouse gas emissions by expanding the use of renewable fuels produced from plants, crops, and biomass. These initiatives, along with emission standards set by the EPA, are crucial in mitigating the impact of VMT on emissions and addressing climate change.
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Frequently asked questions
Greenhouse gas (GHG) emissions from transportation account for about 28% of total US greenhouse gas emissions, making transportation the largest contributor to US GHG emissions. In addition to carbon dioxide (CO2), automobiles using gasoline produce methane (CH4) and nitrous oxide (N2O) from the tailpipe and can emit hydrofluorocarbon (HFC) from leaking air conditioners.
The main pollutant emitted by vehicles is carbon dioxide, which is a greenhouse gas and the most common human-caused greenhouse gas. Other pollutants emitted by vehicles include nitrogen dioxide, carbon monoxide, hydrocarbons, benzene, and formaldehyde.
Vehicles emit pollution through the exhaust pipe, which is a byproduct of the combustion process. Pollution is also emitted through the evaporation of fuel.
