The samples were collected on National Highway 2 to see how much traffic coming in from outside Delhi contributes to the formation of particulate matter.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/significant-traces-lead-ambient-air-samples-iit-study
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/indian-express-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-quality-standards
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/indian-institute-technology-iit
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pm-25
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/respiratory-diseases
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects