This recent study published by Department of environmental sciences, JNU points out alarming levels of aerosol and heavy metals in Delhi's air.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/human-exposure-particulate-matter-and-their-risk-assessment-over-delhi-india
[2] http://admin.indiaenvironmentportal.org.in/category/author/rajesh-kushwaha
[3] http://admin.indiaenvironmentportal.org.in/category/author/himanshu-lal
[4] http://admin.indiaenvironmentportal.org.in/category/author/arun-srivastava-et-al
[5] http://admin.indiaenvironmentportal.org.in/category/journal/national-academy-science-letters
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/heavy-metals
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/urban-air-quality
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-quality-monitoring