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Air Quality and Health Concerns

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Why are diesel emissions such a concern? Emissions from diesel engines contribute to a variety of air quality problems and may affect the health of those living, working and going to school in areas where diesel emissions are present.

Air Quality issues

The Midwest Region has over 28 million people living in areas not meeting the National Ambient Air Quality Standards (NAAQS) for ozone and/or particulate matter (PM 2.5) standards in 2004. These are called nonattainment areas. Emissions from diesel engines contribute to smog (ozone), fine particles like PM2.5, and air toxic air quality concerns.


"mobile source"

Any non-stationary source of air pollution such as cars, trucks, motorcycles, buses, airplanes, and locomotives

Ground-level ozone is the primary component of smog. It is formed from reactions between nitrogen oxides (NOx) and volatile organic compounds (VOC). These pollutants are found in mobile source exhaust.

Particulate Matter

Particulate matter (PM) is chemically and physically diverse; it can exist as liquid droplets or as solid particles. PM is typically classified as either coarse, with a diameter between 2.5 and 10 micrometers (PM10), or fine, with a diameter less than 2.5 micrometers (PM2.5).

Air Toxics

Also known as hazardous air pollutants (HAPs), air toxics from mobile sources are formed because of toxic compounds found in the fuel that either pass through the engine unburned or are created due to incomplete combustion. Twenty-one of the 188 originally-listed HAPs are associated with mobile source emissions - mainly inorganic materials, such as metals and VOCs.

Air toxics (toxic air pollutants)

Health Concerns

Who is affected by diesel emissions?

These health effects are especially significant for sensitive populations such as children, outdoor workers, the elderly and people with respiratory disease.

The various pollutants discussed above may lead to public health problems such as asthma, respiratory and cardiovascular illness and premature death. See Health Assessment Document for Diesel Engine Exhaust (May 2002)


EPA has identified several health impacts of exposure to ozone including increased hospital admissions and emergency room visits for respiratory problems. See Regulatory Impact Analysis: Heavy-Duty Engine and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements (PDF) (19pp, 59K) December 2000

Repeated exposure to ozone can lead to many respiratory system ailments including respiratory infection, lung inflammation and asthma. Prolonged (between 6 and 8 hours), repeated exposure to ozone can cause irreversible changes in lung structure that can lead to premature lung aging. It can also result in chronic illnesses such as emphysema and chronic bronchitis. Furthermore, the full body of evidence in the scientific literature indicates a positive relationship between ozone exposure and premature death.

Particulate Matter

The primary negative health effects linked to PM include premature death, aggravation of cardiovascular and respiratory disease, and changes in lung function and structure. See Regulatory Impact Analysis: Heavy-Duty Engine and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements (PDF) (19pp, 59K) December 2000

Coarse particles are believed to impact respiratory conditions whereas fine particles are more closely tied to premature death and hospital admissions for cardiopulmonary diseases.

Air Toxics

Also known as hazardous air pollutants, air toxic pollutants may cause cancer or other serious health effects such as reproductive problems or birth defects. They also can cause adverse environmental and ecological effects.

Diesel exhaust contains gaseous components like benzene that are known carcinogens in addition to gases that are possible or probable carcinogens (e.g., formaldehyde, 1,3-butadiene). Exposure to diesel exhaust also likely causes other health problems. Acute exposures to diesel exhaust can cause symptoms such as headaches, eye irritation and nausea. Chronic exposure to diesel exhaust constitutes a respiratory system hazard.

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