What’s In Diesel Exhaust?

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Diesel exhaust is a toxic combination of carbon, sulfur and nitrogen particulate matter compounds, trace metals and related gases created from combustion of diesel fuel and the burning of lubricating oil.

Although diesel exhaust contains known carcinogens like benzene and probable carcinogens like formaldehyde, acetaldehyde, 1,3-butadiene, acrolein, and dioxin, particulate matter is often considered the most harmful component of diesel exhaust.

Particulate matter falls into two kinds of categories: fine particles, less than 1 micron (a millionth of a meter) in diameter, and “nanoparticles”, otherwise known as ultrafine particles, under 10-100 nm (billionths of a meter.) Because they are so small these ultrafine particles can easily invade the body’s circulatory system, carrying with them the other toxins in diesel exhaust, adhered to their carbon cores.

Diesel Emissions: Sources

Diesel engines can be found literally anywhere, in everything from ships and trains to school and city buses, construction and agricultural vehicles, long-haul trucks and many other vehicles that surround us on a daily basis.

On-Road/Highway Diesels
This category includes many types of vehicles, such as municipal and commercial trucks and buses. Of the seven million highway diesels on the road today, 400,000 are school buses and 70,000 are transit buses. On-road diesels released 100,000 tons of directly-emitted fine particles in 2002, about one third of the total from diesels.

Non-Road Diesel Engines and Equipment
Non-road vehicles may include construction equipment such as excavators, mining equipment and agricultural machinery. There were approximately six million non-road diesel engines in service in 2003, and in 2002, 155,000 tons or fully half of all the fine particles directly emitted from diesels came from non-road engines.  

Marine and River Diesel Engines
Diesels can often be found in large commercial ships, as well as smaller boats and other water-going vessels. In 2002, marine diesels released 40,000 tons of directly-emitted fine particles, or 13 percent of all diesel fine particles in the U.S.

Locomotive Diesels
Locomotive diesels account for a significant fraction of mobile source emissions in the U.S. today. In many areas, diesel trains travel through and pollute core urban and industrial areas. Diesel locomotives release 20,000 tons of directly-emitted diesel fine particles each year, or six percent of all diesel fine particles. Diesel locomotives are particularly notable because of their long useful life – often lasting 40 years or more – making cleaning up diesels an important priority.