The effects of particulate matter air pollution on respiratory health and on the cardiovascular system
Particulate matter (PM) is a major component of urban air pollution and has a significant effect on human health. Natural PM sources are volcanic eruptions, dust storms, forest and grassland fires, living vegetation and sea spray. Traffic, domestic heating, power plants and various industrial processes generate significant amounts of anthropogenic PM. PM consists of a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air. The chemical composition of particles is very complex and depends on emission sources, meteorological conditions and their aerodynamic diameter. Several epidemiological studies have demonstrated that exposure to PM of varying size fractions is associated with an increased risk of respiratory and cardiovascular diseases. Adverse health effects have been documented from studies of both acute and chronic exposure. The most severe effects in terms of overall health burden include a significant reduction in life expectancy by a several months for the average population, which is linked to long-term exposure to moderate concentrations of PM. Nevertheless, numerous deaths and serious cardiovascular and respiratory problems have also been attributed to short-term exposure to peak levels of PM. Although many studies attribute greater toxicity to smaller size fractions, which are able to penetrate deeper into the lung, the molecular mechanisms and the size fractions of the PM that are responsible for the observed diseases are not completely understood.