While the major air pollution threat in Delhi is from the tiny PM2.5 particles that get embedded in the lungs, during the summer, PM10 is the primary pollutant.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/why-delhi-dust-haze-may-be-here-stay
[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/storms
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pm-25
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rspm-pm-10
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/indian-institute-technology-iit
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/indian-meteorological-department-imd
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/centre-science-and-environment-cse
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/deforestation