The monitoring of air pollution, or air quality, as carried out by Environmental Policy Agencies (EPA’s), and by local councils, industry, research bodies and environmental pressure groups, includes measurements of atmospheric aerosols. These measurements are expressed in terms of particulate matter, also known as particle pollution or PM. Particulate matter is defined as the atmospheric concentration of particles that are 10 micrometers in diameter or smaller – because these generally pass through the throat and nose and enter the lungs – at breathing level.
EPA’s distinct two particulate matter size categories:
- Inhalable coarse particles (or PM2.5-10), such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter.
- Fine particles (or PM2.5), such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air.
Limits for acceptable levels of these atmospheric particles as part of air pollution have been set in order to protect the population from the dangerous effects of pollution on health.