Environmental Protection Agency: Particulate Matter (PM) Basics
Environmental Protection Agency

PM stands for particulate matter (also called particle pollution): the term for a mixture of solid particles and liquid droplets found in the air.

Environmental Protection Agency: Setting and Reviewing Standards to Control Particulate Matter (P...
Environmental Protection Agency

National Ambient Air Quality Standards (NAAQS) for PM pollution specify a maximum amount of PM to be present in outdoor air.