Asia has the world's highest concentration of two and three wheelers, both in absolute terms and as a fraction of overall road vehicle population. In many Asian cities, these vehicles account for 50 to 90% of the total vehicle fleet of which a large percentage are powered by two stroke engines. The main pollutants of concern from 2-stroke three wheelers are hydrocarbons and particulate matter.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/air-pollution-6
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/daily-star-bangladesh
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pollution
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/vehicle-technology
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/transport
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/asia
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/bangladesh
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/india