Where PM Comes From

PM can come from many sources - the dust stirred up while driving on an unpaved road, car exhaust, the application of fertilizer. 

• Primary particles originate directly from sources such as construction sites, fields, fires or sandstorms.  Although the dirt kicked up on a dry soccer field or baseball diamond may not seem like pollution, the particles in the air can have an adverse effect on your health.
   

• Secondary particles form when metals, sulfur dioxides, nitrogen oxides and other chemicals emitted from power plants, factories and cars react with chemicals already in the air.  These secondary particles make up fine PM, or PM 2.5 (meaning the particles measure 2.5 microns in diameter). 

To give some perspective on PM’s size, the average human hair measures 70 microns in diameter, whereas some types of PM measure less than 10 microns.  The smaller the PM, the more harmful, because its size allows it to travel deep into the lungs and even into the bloodstream.