Particulate matter (PM) is a mixture of solid and liquid particles. Because particles originate from a variety of activities and processes, their chemical and physical compositions vary. PM can be directly emitted or can be produced by secondary formation in the atmosphere when gaseous pollutants, such as nitrogen oxides and sulfur dioxide, chemically react with ammonia and other compounds to form fine aerosol particles.
Sources of PM are mainly due to human (anthropogenic) activities caused by area-wide sources, such as residential wood and other fuel combustion smoke and other pollutants, motor vehicles including entrained road dust and exhaust, and off-road mobile sources including dust and equipment exhaust emissions from construction and farming activities. PM can also be generated from natural sources such as windblown dust and wildfires.
Adverse health effects related to particulate matter exposure result in a number of economic costs and social consequences. These include increased medical costs, hospital admissions, work loss days, school absences, caregiver burdens, and premature deaths. Numerous scientific studies have linked particle matter exposure to a variety of health related problems, such as irritation of the airways, coughing, or difficulty breathing, decreased lung function, aggravated asthma, development of chronic bronchitis, irregular heartbeat, and nonfatal heart attacks. People with heart or lung diseases, children and older adults are the most likely to be affected by particle pollution exposure. Studies also indicate that even healthy individuals may experience temporary symptoms from exposure to elevated levels of particle matter.