Air pollution is a major environment-related health threat to children and a risk factor for both acute and chronic respiratory disease. While second-hand tobacco smoke and certain outdoor pollutants are known risk factors for acute respiratory infections, indoor air pollution from biomass fuel is one of the major contributors to the global burden of disease.
Outdoor air pollution is largely and increasingly a consequence of the combustion of fossil fuels for transport, power generation and other human activities. Combustion processes produce a complex mixture of pollutants that comprises both primary emissions, such as diesel soot particles and lead, and the products of atmospheric transformation, such as ozone and sulfate particles formed from the burning of sulfur-containing fuel.
Outdoor air pollution remains a serious problem in cities throughout the world, particularly in the megacities of developing countries and it is estimated that a quarter of the world population is exposed to unhealthy concentrations of air pollutants. Children are particularly at risk due to the immaturity of their respiratory organ systems.
Indoor cooking and heating with biomass fuels (agricultural residues, dung, straw, wood) or coal produces high levels of indoor smoke that contains a variety of health-damaging pollutants. There is consistent evidence that exposure to indoor air pollution can lead to acute lower respiratory infections in children under five, and chronic obstructive pulmonary disease and lung cancer (where coal is used) in adults.
Acute lower respiratory infections, in particular pneumonia, continue to be the biggest killer of young children and cause more than 2 million annual deaths. This toll almost exclusively falls on children in developing countries.