Particulate matter less than 2.5 µm aerodynamic diameter (or, more strictly, particles which pass through a size selective inlet with a 50 % efficiency cut-off at 2.5 µm aerodynamic diameter)

Particulate matter of mass median aerodynamic diameter (MMAD) less than or equal to 2.5 micrometers.

tiny solid or liquid particules, generally soot and aerosols. The size of the particles (2.5 microns or smaller, about 0.0001 inches or less) allows them to easily enter the air sacs deep in the lungs where they may cause adverse health effects; PM2.5 also causes visibility reduction

particulate matter 2.5 micrometers or smaller in diameter

EPA defines PM2.5 as particulate matter with a diameter of 2.5 micrometers collected with 50% efficiency by a PM2.5 sampling collection device. However, for convenience in this reference material, the term PM2.5 includes all particles having an aerodynamic diameter of less than or equal to 2.5 micrometers.

Particles smaller than 2.5 micrometers.

Includes tiny particles with an aerodynamic diameter less than or equal to a nominal 2.5 microns. This fraction of particulate matter penetrates most deeply into the lungs.

Particulate matter smaller than 2.5 microns in size

A USEPA standard that includes additional controls on particulates sized 2.5 micron and smaller

Fine dust and particles where the particles are less than 2.5 micrometers in diameter.

particulate matter smaller than 2.5 microns in diameter

particles less that 2.5 micrometer in diameter, small enough to be inhaled and may reach the lungs. Concentrations greater than 20 µg/m3 are thought to adversely affect pulmonary function.