World’s most polluted cities announced by WHO

India has four of the five cities in the world with the worst air pollution, the World Health Organization announced on Thursday.

Experts at WHO said India faces a "huge challenge" but air pollution in many countries is so bad that they have no monitoring system and cannot be included in the UN agencies ranking.

The city of Zabol in Iran, which suffers from months of dust storms in the summer, has the dirtiest air and recorded a fine particulate matter (PM2.5) measurement of 217.

WHO, which is based in Geneva, Switzerland, said the next four most polluted cities in the world are Gwalior, Allahabad, Patna and Raipur in India.

The Indian capital New Delhi was ranked as the ninth worst city for air pollution, measured by the amount of particulate matter under 2.5 micrograms found in every cubic meter of air, and has an annual average PM2.5 measurement of 122.

New Delhi was ranked as the most polluted city in 2014 with a PM2.5 reading of 153 but officials have introduced measures to tackle pollution including a limit on the use of private cars.

Scientists have found that tiny particulate matter can cause long term health issues such as lung cancer, strokes and heart disease, and can trigger short term symptoms including heart attacks.

More than 7 million premature deaths occur every year worldwide due to air pollution, with 3 million of those due to outdoor air quality, WHO said.

Maria Neira, Head of Public Health, Environmental and Social Determinants of Health at the WHO, said: "Probably some of the worst cities that are the most polluted ones in the world are not included in our list, just because they are so bad that they do not even have a good system of monitoring of air quality, so it’s unfair to compare or give a rank."

WHO conducted a survey of 3,000 urban areas and the data shows only 2 per cent of cities in developing countries have air quality that meets WHO standards, compared to 44 per cent of cities in developed countries.