Particle pollution (also called particulate matter or PM) is the term for a mixture of solid
particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or
smoke, are large or dark enough to be seen with the naked eye. Others are so small, they can
only be detected using an electron microscope.
Particle pollution includes "inhalable coarse particles," with diameters larger than 2.5
micrometers and smaller than 10 micrometers and "fine particles," with diameters that are
2.5 micrometers and smaller. How small is 2.5 micrometers? Think about a single hair from
your head. The average human hair is about 70 micrometers in diameter – making it 30
times larger than the largest fine particle.
These particles come in many sizes and shapes and can be made up of hundreds of
different chemicals. Some particles, known as primary particles are emitted directly from a
source, such as construction sites, unpaved roads, fields, smokestacks or fires. Others form in
complicated reactions in the atmosphere of chemicals such as sulfur dioxides and nitrogen
oxides that are emitted from power plants, industries and automobiles. These particles,
known as secondary particles, make up most of the fine particle pollution in the country.
EPA regulates inhalable particles (fine and coarse). Particles larger than 10 micrometers
(sand and large dust) are not regulated by EPA.
• Health: Particle pollution contains microscopic solids or liquid droplets that are so
small that they can get deep into the lungs and cause serious health problems. The size of
particles is directly linked to their potential for causing health problems. Small particles less
than 10 micrometers in diameter pose the greatest problems, because they can get deep
into your lungs, and some may even get into your bloodstream.
• Visibility: Fine particles (PM2.5) are the major cause of reduced visibility (haze) in
parts of the United States, including many of our treasured national parks and wilderness
• Reducing particle pollution: EPA’s national and regional rules to reduce emissions of
pollutants that form particle pollution will help state and local governments meet the
Agency’s national air quality standards.
• Fine particles are easily inhaled deep into the lungs where they may accumulate,
react, be cleared or absorbed.
• Scientific studies have linked particle pollution, especially fine particles, with a series
of significant health problems, including:
increased respiratory symptoms, such as irritation of the airways, coughing, or difficulty
breathing, for example;
decreased lung function;
development of chronic bronchitis;
nonfatal heart attacks; and
premature death in people with heart or lung disease.
• Particle pollution can cause coughing, wheezing, and decreased lung function even
in otherwise healthy children and adults.
• Studies estimate that thousands of elderly people die prematurely each year from
exposure to fine particles.
• The average adult breathes 3,000 gallons of air per day.
• According to the American Academy of Pediatrics, children and infants are among
the most susceptible to many air pollutants. Children have increased exposure compared
with adults because of higher minute ventilation and higher levels of physical activity.
• Fine particles can remain suspended in the air and travel long distances. For
example, a puff of exhaust from a diesel truck in Los Angeles can end up over the Grand
• Some of the pollutants which form haze have also been linked to serious health
problems and environmental damage.
• Particle pollution settles on soil and water and harms the environment by changing
the nutrient and chemical balance.
• Particle pollution, unlike ozone, can occur year-round.