"India's economic development has led to the worsening of air quality in major Indian cities, according to the results of a survey by The Energy and Resources Institute ( Teri) in Bangalore, Chennai, Delhi, Hyderabad, Kolkata and Mumbai. The transport sector was ranked the highest followed by factories in and around the city as the second highest contributor towards air pollution in Chennai, Delhi, Kolkata, and Mumbai." (Quoted froma article)