Smarter Living: Chemical Index

Diesel engine exhaust from older diesel engines contains a harmful mix of particles and gases, but new diesel engines have advanced pollution controls that eliminate more than 90 percent of this pollution.

What Is It?

Diesel exhaust is shorthand for the wide mix of soot particles, metals, and gaseous chemicals that are emitted from the engines used in most trucks, buses, ships, trains, and even some cars.

Older diesel engines emit huge amounts of diesel exhaust, triggering significant health impacts for millions of Americans and raising community concerns around ports, railyards, schools, and other places that are hotspots for diesel pollution.

Thanks to EPA and California emissions standards implemented since 2007, new diesel engines are more than 90 percent cleaner than the older models. These engines are equipped with advanced filters and catalysts that keep those emissions from our lungs.

Recently, diesel-powered cars have been getting more attention, because, compared to regular gasoline engines, they get better fuel economy and emit less carbon dioxide, a greenhouse gas . These newer diesel cars meet the same emission standards as new gasoline cars (unlike in Europe, where diesel cars don’t have to meet the same standards as gasoline cars).

Health Concerns

Diesel engines--especially older engines--emit large amounts of fine particulate matter (PM). 90 percent of these particles are less than 1 micron in diameter, too small to see (by contrast, the typical human hair is about 70 microns in diameter). These tiny particles evade our respiratory defenses and get stuck in the deepest recesses of our lungs, where they can cross into the bloodstream. Unlike naturally-formed particles in our air, like sand or sea salt, diesel particles carry toxic heavy metals, sulfates, and dozens of other chemicals.

Numerous studies have documented the link between fine particles in the air and increased risk of emergency room visits, hospital admissions, asthma attacks, cardiovascular disease, respiratory disease, adverse birth outcomes, and premature death. Infants, children, the elderly, and people with emphysema, asthma, and chronic heart or lung disease are at higher risk of harm from this particulate pollution.

The exhaust from older diesel engines has been linked to a myriad of health impacts in dozens of studies. Exposure to diesel fumes can irritate the eyes, nose, throat and lungs, and can cause headaches, lightheadedness, and nausea. The exhaust can also worsen asthma attacks and make people who suffer from allergies more sensitive to the substances that trigger their allergies, such as pollen and dust. Exposure to diesel exhaust over a period of years can result in inflammation and long-term lung damage . As a result, people who work in areas of high diesel exposure (e.g., at railyards) are at higher risk of lung cancer.

Several chemicals known to cause cancer in humans are found in diesel exhaust, including arsenic, benzene, and formaldehyde. Diesel exhaust from these older engines has been classified as a Toxic Air Contaminant by the California Air Resources Board and as a probable human carcinogen by the U.S. Environmental Protection Agency.

Diesel engines also emit nitrogen oxides, which are gases that directly irritate the lungs, react in the atmosphere to form the smog-constituent ozone, and even create more particulate matter in the air


People who live near highways and busy roads are most likely to be exposed to high levels of diesel exhaust. EPA estimates approximately 35 million Americans fit this category, by living within 100 yards of busy roads of four lanes or more. Individuals who live near or work at ports, railyards, distribution centers and other diesel "hot spots" also face disproportionate exposure rates and associated health impacts. Toll-booth workers, truck drivers, bus drivers, mechanics, and others who work around diesel engines have some of the highest exposures to the exhaust. Children who ride in older school buses may also be exposed.

Stay Safe

Completely avoiding diesel exhaust is impossible, given the ubiquity of diesel vehicles in our midst. However, you can take steps to reduce your family’s risk. When walking or exercising outdoors, choose a route that avoids major streets or highways where possible. Take your children to playgrounds that are not next to major highways.

Take Action

Protect your kids. If you have school-age children, find out if your state or school has a policy against allowing school buses to idle outside classrooms. To find out if your children’s school buses have been retrofitted to keep diesel exhaust from seeping into the cabin, contact your children’s school district, busing company, or state’s department of environmental protection. Check out Clean School Bus USA, an EPA program to help schools reduce idling, retrofit older buses, and replace buses with ones with pollution controls.

Further, take steps to ensure that new schools and housing developments are not placed near busy roadways, ports, railyards or other industrial areas where the risk of diesel exposure increases.

Don’t buy used diesel cars. Although the fuel economy of diesel cars is attractive, older diesel cars do not have today’s pollution control technologies. New diesel cars are certified to the same emissions standards as comparable gasoline cars.

Consider the pros and cons of biodiesel. On the plus side, biodiesel is made from new or recycled vegetable oils, animal fats, or grease collected from restaurants. It is naturally low in sulfur and emits lower levels of pollutants than petroleum diesel. However, 100 percent biodiesel fuel (B100) gives lower gas mileage than standard diesel made from petroleum, may require modifications to your car’s engine, and does not work well in cold temperatures. More common is B20, a mix of 20 percent biodiesel and 80 percent petroleum diesel, which can be used by most diesel cars.

In addition, biofuel production in certain cases, especially when based on food crops, can impact wildlife habitat, water quality, and the global food supply. NRDC supports the responsible development of biofuels, and has worked with producers to help create markets for locally produced biodiesel from used restaurant and other waste oils. Learn more on NRDC's Switchboard and find out how you can make a difference.

Learn More

For more about the health effects of diesel exhaust, see this fact sheet from the California EPA.

For more about clean diesel, see the US EPA.

To learn about biodiesel, see the U.S. Department of Energy's renewable energy pages.

To learn more about your automobile choices, see NRDC’s overview of green car technologies.

last revised 12/27/2011

Get Updates and Alerts

See the latest issue >

NRDC Gets Top Ratings from the Charity Watchdogs

Charity Navigator awards NRDC its 4-star top rating.
Worth magazine named NRDC one of America's 100 best charities.
NRDC meets the highest standards of the Wise Giving Alliance of the Better Business Bureau.

Donate now >

Share | |
Find NRDC on