India is home to four of the five cities in the world with the worst air pollution, the World Health Organization said on Thursday. India's capital New Delhi was the survey's ninth worst city, measured by the amount of particulate matter under 2.5 micrograms found in every cubic meter of air, with an annual average PM2.5 measurement of 122. Tiny particulate matter can cause lung cancer, strokes and heart disease over the long term, as well as triggering symptoms such as heart attacks that kill more rapidly.
