What PM's Made Of

PM is a mix of solid particles and liquid droplets.  Dust, dirt and soot are some of   the larger (10 microns to 2.5 microns) and more naturally-occurring particles found in the air.  PM smaller than 2.5 microns forms when gases usually composed of metals, sulfur dioxides and nitrogen oxides emitted from factories, power plants and/or cars react with chemicals already in the atmosphere.  This reaction produces tiny particles and droplets suspended in the air.