Degrading air quality in metro cities is a matter of concern for public health. Massive tree plantation drives are often conducted in order to provide oxygen to choking cities.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/deciduous-trees-compound-leaves-more-tolerant-air-pollution-study
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/business-line-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/afforestation
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/trees
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/oxides-nitrogen-nox
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/carbon-dioxide