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In this Thursday, Dec. 15, 2011 photo, a man walks by the Presidential Palace through haze caused by smog in New Delhi, India. A decade ago, plans for a metro and clean-fuel buses were hailed as New Delhi's answer to pollution. But air in the Indian capital is as dirty as ever - partly because its continued development has brought skyrocketing use of cars. (AP Photo/Saurabh Das)

India's air pollution problem

January 1, 1970

New Delhi's citywide pollution sensors routinely register levels of small airborne particles at two or sometimes three times its own sanctioned level for residential areas, putting the city up there with Beijing, Cairo and Mexico City at the top of indexes listing the world's most-polluted capitals.