What is Diesel Particulate Matter?

As part of EPA's National Air Toxics Assessment activities, EPA conducted a national-scale assessment of 33 air pollutants. This is a subset of 32 air toxics on the Clean Air Act's list of 188 air toxics plus diesel particulate matter (diesel PM).

Emissions from diesel vehicles are an important source of both fine particle and gaseous pollution.

As diesel fuel burns in an engine, particles and gases formed by the combustion process travel out the exhaust system of the vehicle.

Unlike, gasoline powered vehicles, which burn fuel more efficiently and have catalytic converters, older diesel engines emit a lot of particulate pollution.

  • Fine particulate matter are so small that several thousand of them could fit onto the head of a pin.
  • Diesel engines are one of the largest sources of fine particulate matter, other than natural sources, such as forest fires.
  • Fine particles in the air are a serious public health problem. They pose significant health risk because they can travel deep into the respiratory system affecting the delicate tissue of the lungs.
  • Fine particles can aggravate respiratory conditions such as asthma and bronchitis, and can even cause lung damage and premature death.

Diesel emissions also contain many polycyclic aromatic hydrocarbons, several of which are suspected of being human carcinogens, absorbed onto particle surfaces.

To learn more about diesel emissions and the steps the U.S. EPA is taking to reduce them, please visit these sites: