Particulate matter (PM) is solid or liquid particles that are suspended in a gas. A good example of PM is smoke, which has its white, grey, or black color from tiny bits of matter. PM impacts more people than any other air pollutant. Major components of PM include sulfate, nitrates, ammonia, sodium chloride, carbon, mineral dust, and water. When people breathe, PM can enter deep into the lungs where it can cause serious problems. It can even enter the bloodstream from the lungs and can thus affect the heart. PM is responsible for millions of premature deaths every year (up to 3.2 million worldwide). PM can also have a warming effect on the climate. According to a recent study, the major component of PM called black carbon or soot is now officially the second-most significant cause of climate change after carbon dioxide. (see page on carbon dioxide for more information about climate change).
The ability of PM to impact human health depends on the size of the particles. PM is generally grouped into three size categories. PM10 refers to PM that has a diameter of 10 micrometers and smaller, about one seventh the diameter of a human hair. PM2.5 refers to PM that has a diameter of 2.5 micrometers and smaller, about one thirtieth the diameter of a human hair. The third category is ultrafine particles (UFP), which refers to particles that have a diameter of less than one tenth of a micrometer.
People with heart or lung diseases, the elderly, and children are especially at risk to the health effects of PM. PM has been linked with the following health effects according to the USEPA:
- Premature death in people with heart or lung disease
- Nonfatal heart attacks
- Irregular heartbeat,
- Aggravated asthma
- Decreased lung function, and
- Increased respiratory symptoms, such as irritation of the airways, coughing, or difficulty breathing.
PM also creates the reduced visibility known as haze, and can have other strong environmental effects such as creating acid rain, changing the nutrient balance in rivers and the coastal oceans, depleting the nutrients in soil, and damaging plants and trees in agriculture and in natural forestlands.