Top 20 most polluted cities in the world
May 8, 2014 -- Updated 1003 GMT (1803 HKT)
STORY HIGHLIGHTS
- Delhi is most polluted city in the world in PM2.5 concentrations
- Half of the top 20 most polluted cities were in India, according to data
- PM2.5 is considered most harmful to health
Delhi has the highest
level of the airborne particulate matter, PM2.5 considered most harmful
to health, with 153 micrograms. Not far behind is another Indian city,
Patna with 149 micrograms. These figures are six times what the WHO
considers a "safe" limit -- which is 25 micrograms.
Half of the top 20 cities
in the world with the highest levels of PM2.5 were in India, according
to the pollution data released by the WHO, which included 1,600 cities.
Other cities with high levels were located in Pakistan and Bangladesh.
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PM2.5 refers to the
diameter measured in microns of particulates such as ammonia, carbon,
nitrates and sulfate -- which are small enough to pass into the
bloodstream and cause diseases such as emphysema and cancer.
The WHO data echoes an earlier study this year which found that air pollution in New Delhi is now worse than Beijing.
No Chinese cities ranked
in the top 20 most polluted cities, despite thick, gray smog filling its
cities and millions of residents commuting behind surgical masks.
Beijing reported 56 micrograms of PM2.5. This year, Chinese leaders have
declared "war on pollution."
Delhi has been described
as having weak enforcement of pollution controls by India's Center for
Science and Environment, a public interest group.
"Originally designed as
compact entities to reduce the length of travel ... (Indian cities) are
becoming victims of killer pollution, congestion ... and a crippling
car-dependent infrastructure," according to the group.
Air pollution has spread
by increasing reliance on fossil fuels, coal-fired power plants, cars
and the use of biomass for cooking and heating.
Cities with the lowest level of pollution were located in Canada, the United States, Finland, Iceland and Sweden.
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