How Much Air Pollution Comes From Cars?

When vehicles burn gasoline made from fossil fuels, they release pollutants in the form of nitrogen dioxide, carbon dioxide, hydrocarbons, sulfur oxides, and particulate matter directly into the air. Pollutants caused by these kinds of emissions have been connected with negative impacts on human health—especially when exposed over long periods of time or in high concentrations—as well as climate change and environmental issues.

According to the United States Environmental Protection Agency (EPA), motor vehicles produced about 22% of total U.S. greenhouse gas (GHG) emissions in 2020, making them the most significant contributor to the country’s emissions. Even worse, GHG emissions in the transportation sector increased more than any other sector between 1990 and 2019.

Car Air Pollution

Burning fossil fuels, like gasoline and diesel, release greenhouse gases that build up in the Earth’s atmosphere leading to warming climates and extreme weather events that can displace wildlife populations, destroy habitats, and contribute to rising ocean levels. Air pollution can also negatively influence the soil and water quality in the natural environment.

Apart from what comes out of your car’s tailpipe, the environmental cost of extracting these fossil fuels is also high. Not to mention, vehicle manufacturing from producing materials like plastic, paint, and rubber can contribute to pollution before cars even hit the road. Even gasoline fumes that escape into the air when we pump into our fuel tanks play a part in air pollution.

Likewise, the disposal of old cars (typically compacted into a dump after being stripped for parts) has an impact on the environment since different parts of the car take various times to decompose. Studies have also suggested that asphalt could be a long-lasting source of pollution.

Carbon Dioxide

The EPA says that carbon dioxide emissions (which has been linked to climate change time and time again) in the United States increased by about 3% between 1990 and 2019, corresponding with factors like population growth, economic growth, changing behaviors, new technologies, and increased demand for travel.

As the greatest source of greenhouse gas emissions in the country, 6,558 million metric tons of CO2 were emitted in the U.S. in 2019, accounting for 80% of total GHG emissions.

Particulate Matter

Particulate matter, also known as particle pollution or PM, refers to the mixture of solid particles and liquid droplets that are small enough to be inhaled and cause health problems in humans and animals. Most of these particles form in the atmosphere as a result of reactions between chemicals like sulfur dioxide and nitrogen oxides emitted from cars.

Due to their size, particles can travel over long distances by wind before settling on land or water, making bodies of water more acidic, changing nutrient balance in soil, damaging diversity in sensitive ecosystems, and even contributing to acid rain.

Nitrogen Dioxide

Nitrogen dioxide, or NO2, is part of a highly reactive group of gases known as nitrogen oxides (NOx) that primarily reach the air from the burning of fuel. This can contribute to particulate matter and ozone, which are both harmful when inhaled.

Both NO2 and NOx can form acid rain when they interact with water, oxygen, and other chemicals in the atmosphere, but also affect air visibility and contribute to nutrient pollution in coastal water.

The Worst Offenders

A 2015 study conducted by the University of Toronto measured at least 100,000 vehicles using air monitoring probes on one of Toronto’s busiest roadways. Researchers found that the bottom 25% of the cars were responsible for 90% of the total emissions, specifically, 95% of black carbon (soot), 93% of carbon dioxide, and 76% of VOCs including benzene, toluene, ethylbenzene, and xylenes.

Among factors like age and type of car, exhaust pollution also varied depending on acceleration and how the car was maintained. The study presented a method for identifying and targeting the worst vehicle offenders in air pollution, including older cars and cars that hadn’t been adequately cared for.

While greenhouse gases like methane and nitrous oxide from vehicle tailpipes and hydrofluorocarbon from leaking air conditioners have a potential for contributing to climate change, experts agree that carbon dioxide is the worst offender. A typical passenger vehicle emits around 4.6 metric tons of carbon dioxide every year depending on the car’s fuel type, fuel economy, and number of miles driven.

According to the U.S. Energy Information Administration, burning a gallon of gasoline produces about 19.5 pounds of carbon dioxide, and in 2019, the total U.S. CO2 emissions from motor vehicles was 1,139 million metric tons (or just under 22% of the total U.S. energy-related CO2 emissions).

In contrast, a standard compact to midsize car will emit just 6.5 pounds of NOx and 0.4 pounds of PM over a full 12,000 miles of travel (the average car travels 11,467 miles each year).

Outlook

Air pollution from fine particulate matter and fossil fuel combustion contributed to 8.7 million premature human deaths in 2018, or about 1 in 5 deaths worldwide. Air quality may worsen as urbanization expands and creates more traffic congestion near homes and workplaces (In 2018, more than half of the global population lived in cities, though that number is expected to rise to two-thirds by 2050).

Climate models have already set the stage for 5 °C of global warming by the end of the century, so environmental ramifications of vehicle-derived air pollution stand to fare equally as poorly should nothing change.

In 2021, the EPA announced plans to overhaul pollution standards for both passenger cars and heavy-duty trucks to secure pollution reductions for vehicles manufactured starting in 2026. The EPA estimates that the proposal, which revised standards set by the previous administration, would result in a 2.2 billion ton reduction of CO2 emissions through 2050—equal to one year’s worth of GHG emissions from all petroleum combustion in the United States and saving American drivers between $120 to $250 billion in fuel costs.

Electric vehicles will be a big part of worldwide efforts to end air pollution from cars. It’s no secret that EVs produce fewer emissions than conventional vehicles, there are even fuel-efficient cars that use less gas to travel the same distance and cleaner fuels out there that can produce fewer emissions when they’re burned. A 2020 study over 59 different regions found that driving an electric car is better for the environment than driving a gasoline-powered car in 95% of the world.

The good news is that we’ve already seen the potential for improvements in air quality and reductions in global carbon dioxide emissions during 2020-2021. While a majority of the world’s population was instructed to stay at home and off the roads, CO2 emissions went down temporarily by as much as 26% in some parts of the globe and 17% overall.

Correction—August 18, 2022: A previous version of this article mistakenly equated the emissions from the transportation sector with those from just motor vehicles.