This page is a part of our series on each of the criteria air pollutants. Click here to learn more about air quality and air pollutants.
The size of particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 10 micrometers in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects.
EPA groups particle pollution into two categories:
- PM10, aka, “inhalable coarse particles,” such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter.
- PM2.5, aka, “fine particles,” is that which is found in smoke and haze. These particles are 2.5 micrometers in diameter and smaller. PM2.5 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.
There is no safe level of exposure to particle pollution. To reduce the health problems for those living in areas with particle pollution problems, EPA established two separate numerical standards for short term and long term particle pollution.
These standards determine the maximum allowable concentrations of particle pollution. The annual standard is based on particle pollution concentrations measured over 365. The daily standard is based on the average particle pollution concentrations over a 24 hour period. For both standards, regulators average air quality monitor data form the most recent three years to determine if there has been a violation of the allowable levels.