Particulate matter (PM) is the term for small particles found in the air including dust, dirt, soot, smoke, and liquid droplets. Particles can be suspended in the air for long periods of time. Some particles are large or dark enough to be seen as soot or smoke. Others are so small that individually they can only be detected with an electron microscope. Some particles are directly emitted into the air while others are formed in the air through chemical reactions. Sources of PM include cars, trucks, buses, factories, construction sites, tilled fields, unpaved roads, construction, wood burning, agricultural burning, wildfires, prescribed fires, and natural windblown dust.
Particulate matter is a criteria pollutant that comes in a wide range of sizes. Particles less than 10 micrometers in diameter tend to pose the greatest health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter are referred to as fine particles. Sources of fine particles include all types of combustion (e.g., motor vehicles, power plants, and wood burning) and some industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as coarse. Sources of coarse particles include crushing or grinding operations and dust from paved or unpaved roads.
Health Impacts of Exposure
Both fine and coarse particles can accumulate in the respiratory system and are associated with numerous health effects. Coarse particles can aggravate respiratory conditions such as asthma. Exposure to fine particles is associated with several serious health effects, including premature death. Adverse health effects have been associated with exposures to PM over both short periods (such as a day) and longer periods (a year or more).
- When exposed to PM, people with existing heart or lung diseases—such as asthma, chronic obstructive pulmonary disease, congestive heart disease, or ischemic heart disease—are at increased risk of premature death or admission to hospitals or emergency rooms.
- Older persons are especially sensitive to PM exposure. They are at increased risk of admission to hospitals or emergency rooms and premature death from heart or lung diseases.
- When exposed to PM, children and people with existing lung disease may not be able to breathe as deeply or vigorously as they normally would, and they may experience symptoms such as coughing and shortness of breath.
- PM can increase susceptibility to respiratory infections and can aggravate existing respiratory diseases, such as asthma and chronic bronchitis, causing more use of medication and more doctor visits.