Ozone is a highly reactive molecule made of three oxygen atoms. Ozone that forms naturally in the Earth’s upper atmosphere (stratosphere) absorbs most of the sun’s radiation. In the Earth’s lower atmosphere (troposphere), ozone forms as a result of manmade pollution. When ozone forms in the troposphere it can lead to health complications.

Particulate matter (PM) 2.5 is the term used to describe particle pollution found in the air that is smaller than 2.5 micrometers. Manmade and natural sources emit particles of dust, dirt, soot, smoke and other pollutants that are suspended in the air. Particle pollution can cause smog and lead to health complications when inhaled.