A study conducted by Nasa
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/motor-vehicles-biggest-pollutantsmotor-vehicles-biggest-pollutants
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/asian-age-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/vehicular-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-change
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/global-warming
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/asian-age-new-delhi
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/nasa
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/public-transport
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/vehicle-technology-and-fuel