4 out of top 5 world's most polluted cities in India

World Health Organization has said that India is home to four of the five cities in the world with the worst air pollution. But while WHO experts acknowledge India faces a huge challenge, many countries are so bad that they have no monitoring system and cannot be included in its ranking. The dirtiest air was recorded at Zabol in Iran, which suffers from months of dust storms in the summer. The next four are all Indian cities - Gwalior, Allahabad, Patna and Raipur. India's capital New Delhi is the ninth worst city, measured by the amount of particulate matter under 2.5 micrograms found in every cubic metre of air. Maria Neira, head of public health, environmental and social determinants of health at the WHO, praised India's government for developing a national plan to deal with the problem when others have been unable to.