Air pollution is a broad term applied to any chemical, physical, or biological agent that modifies the natural characteristics of the atmosphere. Examples include particulate matter and ground-level ozone.
Air pollutants fall into four main categories: criteria air contaminants, persistent organic pollutants, heavy metals and toxics. Individual pollutants differ from one another in their chemical composition, reactions with other chemicals, sources, persistence, ability to travel through the atmosphere, and impacts.
Air pollution may possibly harm populations in ways so subtle or slow that they have not yet been detected. For that reason research is now under way to assess the long-term effects of chronic exposure to low levels of air pollution—what most people experience—as well as to determine how air pollutants interact with one another in the body and with physical factors such as nutrition, stress, alcohol, cigarette smoking, and common medicines. Another subject of investigation is the relation of air pollution to cancer, birth defects, and genetic mutations.
§ Fine particulate matter and ground level ozone (O3) can affect human respiratory and cardiovascular systems. The young, the elderly and those with cute illness are at greater risk of such effects. PM2.5 and ground level O3 have been associated with hospitalizations, increased respiratory and cardiovascular mortality, asthma exacerbation, decreased lung function, lung inflammation and changes in heart rate variability. In 2009, 8.1% of Canadians 12 years and older had been diagnosed with asthma by a health professional. This rate did not significantly change from 2001 to 2009.
§ Impacts range from minor breathing problems to premature death. The more common effects include changes in breathing and lung function, lung inflammation, and irritation and aggravation of existing heart and lung conditions. There is no safe level for PM2.5 and O3 that does not pose risks to human health.
§ Negative health effects increase as the concentrations of pollutants in the air increase. Even modest increases in concentration can cause small but measurable increases in emergency room visits, hospital admissions, and premature death.