Particulate matter (PM) is a mixture of airborne solid particles and liquid droplets that can be inhaled and may cause serious health problems. PM includes particles with different characteristics (e.g., shape, optical properties, size and composition), but it is most commonly divided into sub-categories based on the particle size information.
Different PM categories are usually reported under the common nomenclature of PMx, where x defines the maximum particle diameter in the airborne particle mixture or aerosol. For example, PM2.5 defines inhalable particles with a diameter of generally 2.5 µm and smaller, PM10 particles with a diameter of 10 µm and smaller, and so forth. The specific PM categories of PM10 and PM2.5 have been historically identified by national governments as important monitoring levels in order to assess the quality of the air we breathe.1,2 PM10 particles irritate exposed mucous such as the eyes and throat, while PM2.5 particles travel all the way through the lungs into the alveoli.