Complex mixture of solid and liquid particles
Composed of many different compounds
Both a primary and secondary pollutant
Sizes vary tremendously
Forms in many ways
Clean-air levels are < 5 µg/m3 *
Background concentrations can be higher due to dust and smoke
Concentrations range from 0 to 500+ µg/m3 *
Health concerns
Can aggravate heart diseases
Associated with cardiac arrhythmias and heart attacks
Can aggravate lung diseases such as asthma and bronchitis
Can increase susceptibility to respiratory infection