PM10 is particulate matter 10 micrometers or less in diameter. These include airborne irritants such as dust, inhalable particles, smoke and mist.

High levels of PM10 particles in the air can irritate the eyes and throat. People with existing heart or lung conditions (including asthma and COPD) can experience an increase in symptoms, including wheezing, chest tightness and difficulty breathing.

PM2.5 particles are small enough to be breathed deep into the lungs. These include fires, power plant emissions and the burning of rubber and plastic. People with chronic respiratory conditions are more sensitive to the effects of breathing in fine particles.