Diesel particulate matter

Diesel particulate matter (DPM) refers to the particulate components of diesel exhaust, which include diesel soot and aerosols such as ash particulates, metallic abrasion particles, sulfates, and silicates. When released into the atmosphere, DPM can take the form of individual particles or chain aggregates, with most in the invisible sub-micrometre range of 100 nanometers.

Health risks
The main particulate fraction of diesel exhaust consists of small particles. Because of their small size, inhaled particles may easily penetrate deep into the lungs. The rough surfaces of these particles makes it easy for them to bind with other toxins in the environment, thus increasing the hazards of particle inhalation. Exposures have been linked with acute short-term symptoms such as headache, dizziness, light-headedness, nausea, coughing, difficult or labored breathing, tightness of chest, and irritation of the eyes and nose and throat. Long-term exposures can lead to chronic, more serious health problems such as cardiovascular disease, cardiopulmonary disease, and lung cancer.

Exposure to diesel exhaust and DPM is a known occupational hazard to truckers, railroad workers, and miners using diesel-powered equipment in underground mines. Adverse health effects have also been observed in the general population at ambient atmospheric particle concentrations well below the concentrations in occupational settings.

Recently, concerns have been raised in the U.S. regarding children's exposure to DPM as they ride diesel-powered schoolbuses to and from school. The Environmental Protection Agency (EPA) has established the Clean School Bus USA initiative in an effort to unite private and public organizations in curbing student exposures.

Regulation
Although the American Mine Safety and Health Administration issued a health standard in January 2001 designed to reduce exposure in underground metal and nonmetal mines, on September 7, 2005, MSHA published a notice in the Federal Register proposing to postpone the effective date from January 2006 until January 2011.