Particle pollution, also known as particulate matter or PM, is a general term for a mixture of solid and liquid droplets suspended in the air. Particle pollution comes in many sizes and shapes and can be made up of a number of different components, including acids (such as sulfuric acid), inorganic compounds (such as ammonium sulfate, ammonium nitrate, and sodium chloride), organic chemicals, soot, metals, soil or dust particles, and biological materials (such as pollen and mold spores).
Particles that are 10 micrometers (µm) in diameter or smaller pose the greatest problems. These smaller particles generally pass through the nose and throat and enter the lungs. Once inhaled, these particles can affect the lungs and heart and cause serious health effects in individuals at greatest risk, such as people with heart or lung disease, people with diabetes, older adults and children (up to 18 years of age). Larger particles (> 10 µm) are generally of less concern because they usually do not enter the lungs, although they can still irritate the eyes, nose, and throat.
Particles of concern can be grouped into two main categories:
- Coarse particles (also known as PM10-2.5): particles with diameters generally larger than 2.5 µm and smaller than, or equal to, 10 µm in diameter. Note that the term large coarse particles in this course refers to particles greater than 10 µm in diameter.
- Fine particles (also known as PM2.5): particles generally 2.5 µm in diameter or smaller. This group of particles also encompasses ultrafine and nanoparticles which are generally classified as having diameters less than 0.1 µm.
Some particles, known as primary particles, are emitted directly from a source, such as construction sites, unpaved roads, smokestacks or fires. Other particles, known as secondary particles, form in complicated atmospheric reactions involving chemicals such as sulfur dioxides and nitrogen oxides that are emitted from power plants, industries and automobiles. Secondary particles make up most of the fine particle pollution in the United States.
Cooking, smoking, dusting, and vacuuming can also produce particle pollution, particularly in indoor settings. Particles produced by combustion are more likely to be fine particles, while particles of crustal (earth) and biological origin are more likely to be coarse particles.
Particulate matter contains microscopic solids or liquid droplets that are so small that they can be inhaled and cause serious health problems. Some particles less than 10 micrometers in diameter can get deep into your lungs and some may even get into your bloodstream. Of these, particles less than 2.5 micrometers in diameter, also known as fine particles or PM2.5, pose the greatest risk to health.
Fine particles are also the main cause of reduced visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas.
Learn more about health and environmental effects
EPA regulates inhalable particles. Particles of sand and large dust, which are larger than 10 micrometers, are not regulated by EPA.
EPA’s national and regional rules to reduce emissions of pollutants that form PM will help state and local governments meet the Agency’s national air quality standards.
Learn about how air quality standards help reduce PM.
You can use air quality alerts to protect yourself and others when PM reaches harmful levels:
Every day the Air Quality Index (AQI) tells you how clean or polluted your outdoor air is, along with associated health effects that may be of concern. The AQI translates air quality data into numbers and colors that help people understand when to take action to protect their health.
- Go to About AirNow to learn how you can get AQI notifications.
- Also learn how the Air Quality Flag Program can help air agencies, schools, and other community organizations to notify their citizens of harmful conditions and adjust outdoor physical activities as needed.