Nearly half of all Americans — more than 147 million — live in counties in the U.S.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/state-air-2014-shows-half-us-lives-unhealthy-air
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/environment-news-network
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/united-states-america-us
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/lung-cancer
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/ozone
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/asthma
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-change
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/respiratory-diseases