The cities with the most polluted air on the planet are in Iran, Mongolia, India, Pakistan and Botswana, while Canada and the United States have those with the least polluted air, according to figures released by the World Health Organization (WHO) yesterday. The organization urges countries with high pollution rates to monitor and manage their environments and bring down the rates of premature deaths and illness.

The new figures relate to the WHO’s first global survey of air pollution, which measures PM10 particle concentration in over 1,000 cities worldwide. These fine particles have a diameter of 10 micrometers or less and when they are inhaled they can enter the bloodstream and cause heart disease, lung cancer, asthma and acute infections of the lower respiratory tract.

Persistently high levels of fine particle pollution are present in many cities, and while this mostly comes from power plants and motor vehicles, other sources also contribute.

In 2008, the WHO estimates 1.34 million people died prematurely as a result of air pollution in cities worldwide. This is up from the 1.15 million deaths estimated for 2004.

In both developed and developing countries, the WHO says the largest sources of urban outdoor air pollution are motor vehicles, small-scale manufacturing and other industries, coal-fired power plants and the burning of biomass or coal for cooking and heating. Wood and coal burning to heat homes, especially in colder months, is also an important contributor, they add.

Dr Maria Neira, WHO Director for Public Health and Environment, told the press that:

“Across the world, city air is often thick with exhaust fumes, factory smoke or soot from coal burning power plants. In many countries there are no air quality regulations and, where they do exist, national standards and their enforcement vary markedly.”

The WHO guidelines for air quality suggest an annual average PM10 of no more than 20 micrograms per cubic metre (µg/m3). Their latest figures show that the majority of cities are above this level. If all cities had met the guideline, the WHO estimates over 1 million premature deaths could have been prevented.

Some cities have an annual average over ten times the guideline limit. These are:

  • In Pakistan: Lahore (200 µg/m3), Peshawar (219), Quetta (251).
  • In Iran: Yasouj (215), Kermanshah (229), Sanandaj (254), Ahwaz (372).
  • In India: Ludhiana (251).
  • In Mongolia: the capital Ulaanbaatar (279).
  • In Botswana: the capital Gabarone (216).

For many of these cities, the main cause of the high air pollution is heavy industry and low-quality vehicle fuel. But for others, such as Ulaanbaatar, the capital of Mongolia and home to nearly half the country’s 2.75 million people, there is an added problem stemming from nomadic herders and farmers leaving their rural lives in tents with no heating and electricity to live in the city where they rely on burning coal, wood and dried dung for cooking and warmth.

The WHO figures show there are over 400 cities with annual average PM10 levels below the 20 µg/m3 guideline. At the top of the list are cities like Whitehorse (3 µg/m3), Kitimat (4), Burns Lake (5) and Houston (5) in Canada, and Clearlake Calif (6) and Santa Fe, New Mex (6) in the United States.

In fact Canada and the US dominate the list of 84 cities that have an annual average PM10 level of 11 µg/m3 and under. The only cities in at the top that aren’t in Canada or the US include Tallinn, the capital of Estonia, and Pekanbaru, the capital of Riau province in Indonesia on the island of Sumatra.

However, more than 10% of the 1,000 or so cities listed in the WHO’s latest survey have an annual average of 70 µg/m3 of PM10.

A reduction from this level to 20 µg/m3 of PM10 could result in a 15% reduction in premature deaths, estimate the WHO, who call for a greater awareness of the health risks caused by urban air pollution and for countries urgently to implement effective policies and close monitoring of the air pollution in their cities.

Neira said:

“Air pollution is a major environmental health issue and it is vital that we increase efforts to reduce the health burden it creates.”

“If we monitor and manage the environment properly we can significantly reduce the number of people suffering from respiratory and heart disease, and lung cancer,” she urged.

Written by Catharine Paddock PhD