Air pollution: Why and how it kills

* Air pollution is responsible for about one in every nine deaths annually, with almost two-thirds of those deaths in the Western Pacific and Southeast Asia, the WHO says.

* By 2040, Asia will account for almost 90 percent of the rise in premature deaths attributable to air pollution.

* Ninety-four percent of deaths are due to non-communicable diseases such as cardiovascular problems, stroke, chronic obstructive pulmonary disease and lung cancer.

* Air pollution also increases the risk of acute respiratory infections.

* Major sources of outdoor air pollution include fuel use by vehicles, dust from construction and landfill sites, coal-fired power plants, agriculture and waste-burning.

* Air pollution comes in many forms. Two particle sizes are widely monitored: PM10, coarse particles of 10 microns or less in diameter; and PM2.5, fine particles of 2.5 microns or less in diameter.