Air pollution – indoor and outdoor – killed an estimated 6.5 million people in 2012, the latest data from the World Health Organization (WHO) shows.
Exposure to high levels of air pollution, especially over the long term, can affect human respiratory and inflammatory systems, and can also lead to heart disease and cancer.
Scientists also say air pollution, caused largely by burning fossil fuels, not only contributes to climate change but is also exacerbated by it, as air stagnation linked to warmer, drier conditions allows soot, dust and ozone to build up in the lower atmosphere.
Here are some key facts about air pollution:
* 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.
* PM2.5, about one-thirtieth of the width of a human hair, can penetrate deep into the lungs and the cardiovascular system, posing the greatest risks to human health.
* Only one in 10 people lives in a city that complies with the WHO air quality guidelines, which is a PM2.5 annual average of 10 microgrammes per cubic metre (µg/m3).
* The air pollution in Delhi is 12.2 times the WHO safe level, while in Beijing it is 8.5 times higher.
* As millions more people move to cities in the coming decades, the number of people exposed to dangerous levels of air pollution will increase.
* In 2013, exposure to outdoor and household air pollution cost global labour income losses of $225 billion. Lost income for South Asian countries alone topped $66 billion.
* It is projected that global healthcare costs related to air pollution will increase to $176 billion in 2060, from $21 billion in 2015.
* The annual number of lost working days due to sickness linked to air pollution is projected to reach 3.7 billion for the world in 2060, up from 1.2 billion now.
* The cost of air pollution – as a result of reduced labour productivity, additional health expenditure and crop yield losses – could lead to annual economic costs of 1 percent of global GDP by 2060. Sources: WHO, World Bank, Asian Development Bank, Clean Air Asia, International Energy Agency, U.S. Environmental Protection Agency, UK Department for Environment, Food & Rural Affairs, Natural Resources Defense Council, Organisation for Economic Co-operation and Development