Particulate matter (PM)

What it is: PM refers to tiny particles in the air that can come from sources such as dust, pollen, and combustion emissions. There are different classifications of PM based on the size of the particles, the most common being 2.5 and 10. The 2.5 refers to the diameter of the particles being less than 2.5 microns (compare with human hair at 100 microns thick).

Sources in Schools: The fine particulate matter (PM 2.5) may come from diesel engines such as those in trucks, school buses, or other construction vehicles. (Source EPA Indoor Air Quality Action Kit)

Health Effects: PM can contribute to a number of health conditions such as lung disease, asthma, and other respiratory conditions. (Source EPA Indoor Air Quality Action Kit)

Devices and Measures

Particle Sensors

PM can be measured using a device called a particulate matter sensor or other air quality monitors. PM2.5 is often measured in micrograms per cubic meter of air, or µg/m³.

Build Your Own Particle Sensor

The EPA has developed hands-on activities for teachers and students that include a particlate matter (PM) sensor kit that can be built by students. Activities are targeted to grades 5-12 and make use of Arduino boards and programming.

View the activities here.

2.5 and 10 Micrometers

The size of particulate matter (PM) is measured in micrometers. There are two main categories of particulate matter: particles measuring less than 2.5 micrometers in diameter (PM2.5), and particles measuring less than 10 micrometers in diameter (PM10).

As seen in the image to the right, both of these particle sizes are less than the diamater of an average human hair (which normally falls in the range of 50-70 micrometers).

Image from EPA Build your Own Particle Sensor

PM2.5 - 1998

Concentrations of PM2.5 in global air from 1998.

Source: Image created by the Center for Intranational Earth Science Information Network

PM2.5 - 2019

Concentrations of PM2.5 in global air from 2019.

Source: Image created by the Center for Intranational Earth Science Information Network

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