Particulate Matter

What is Particulate Matter (PM)?

PM, also known as particle pollution, refers to 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, while other fine particles, such as acids, organic chemicals, metals, soil and dust particles and allergens, are so small they can only be detected by using an electron microscope.

With diameters of 2.5 micrometers and smaller, a size nearly 30 times smaller than a single strand of human hair, fine airborne particles come from a variety of sources including motor vehicles, power plants, wood burning stoves and fireplaces, forest fires and some industrial processes.

What health effects are associated with PM?

Because of their minuscule size, fine particles can travel deep into the lungs, and in some cases, the bloodstream, causing serious health problems. Scientific studies have linked particle pollution exposure to a variety of health conditions including:

irritation of the airways, coughing or difficulty breathing;
decreased lung function;
aggravated asthma;
development of chronic bronchitis;
irregular heartbeat;
heart attacks; and
premature death in people with heart or lung disease.

Why are PM forecasts important?

By checking PM forecasts each day, individuals can stay informed and modify their schedules to reduce their time outdoors and avoid strenuous outdoor activities on days when elevated PM levels are expected.

How are PM levels forecasted?

PM forecasts use the same format as the Environmental Protection Agency’s Air Quality Index (AQI), which is used by state and local agencies to issue public reports of actual levels of particles, ground-level ozone and other common air pollutants. When air quality is good or moderate, and the AQI is 0-100, there are no health concerns related to PM. However, when air quality is in the unhealthy, very unhealthy or hazardous range, the AQI is 101-500, and health concerns with PM increase.

Particulate Matter - Air Quality Index (AQI) and Health Concerns

AQI Values	Air Quality Descriptor	Health Concerns*
AQI Values	Air Quality Descriptor	PM_2.5	PM₁₀
0-50	Good	None	None
51-100**	Moderate	None	None
101-150	Unhealthy for Sensitive Groups	People with respiratory or heart disease, the elderly, and children should limit prolonged exertion.	People with respiratory disease, such as asthma, should limit outdoor exertion.
151-200	Unhealthy	People with respiratory or heart disease, the elderly, and children should avoid prolonged exertion; everyone else should limit prolonged exertion.	People with respiratory disease, such as asthma, should avoid outdoor exertion; everyone else, especially the elderly and children, should limit prolonged outdoor exertion.
201-300	Very Unhealthy	People with respiratory or heart disease, the elderly, and children should avoid any outdoor activity; everyone else should avoid prolonged exertion.	People with respiratory disease, such as asthma, should avoid any outdoor activity; everyone else, especially the elderly and children, should limit outdoor exertion.
301-500	Hazardous	Everyone should avoid any outdoor exertion; people with respiratory or heart disease, the elderly, and children should remain indoors.	Everyone should avoid any outdoor exertion; people with respiratory disease, such as asthma, should remain indoors.

^* PM has two sets of cautionary statements, which correspond to the two sizes of PM that are measured:

	Particles up to 2.5 micrometers in diameter (PM_2.5) Particles up to 10 micrometers in diameter (PM₁₀)
**	An AQI of 100 for PM_2.5 corresponds to a PM_2.5 level of 40 micrograms per cubic meter (averaged over 24 hours). An AQI of 100 for PM₁₀ corresponds to a PM₁₀ level of 150 micrograms per cubic meter (averaged over 24 hours).

About Air Pollution Subcategories

Air Pollution Basics
• What is Ozone?
• Sources of Ozone
• Ozone Formation

Air Quality Facts

Health Effects of Ozone
• St. Louis Population with
Lung Disease
• How Healthy Adults are
Affected by Ozone
• Tips for Exercisers
• Ozone & Hospital
Admissions

Particulate Matter

Local Air Quality
• St. Louis Monitor Map

Air Quality Index

Air Quality Data