The index measures the presence of fine particulate matter known as PM2.5, a pollutant that can fester deep in the lungs and bloodstream of human beings
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/7-top-10-most-polluted-cities-world-are-india-gurgaon-top
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/business-standard-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pm-25
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/world-bank
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-quality-monitoring
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/forest-fires