The World Health Organization says air pollution in many of the world's cities is breaching its guidelines.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/air-pollution-too-high-most-worlds-cities
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/bbc-uk
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/who
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pm-25
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rspm-pm-10
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/children
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/women
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/south-asia
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pakistan
[12] http://admin.indiaenvironmentportal.org.in/category/thesaurus/peshawar
[13] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi
[14] http://admin.indiaenvironmentportal.org.in/category/thesaurus/india
[15] http://admin.indiaenvironmentportal.org.in/category/thesaurus/brazil
[16] http://admin.indiaenvironmentportal.org.in/category/thesaurus/heart-diseases
[17] http://admin.indiaenvironmentportal.org.in/category/thesaurus/respiratory-diseases
[18] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cancer
[19] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-quality-monitoring