High concentrations of ozone in the troposphere are toxic and act as a greenhouse gas. Anthropogenic emissions of ozone precursors have caused widespread increases in ozone concentrations since the late 1800s, with the fastest-growing ozone precursor emissions currently coming out of east Asia.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/increasing-springtime-ozone-mixing-ratios-free-troposphere-over-western-north
[2] http://admin.indiaenvironmentportal.org.in/category/author/o-r-cooper
[3] http://admin.indiaenvironmentportal.org.in/category/author/d-d-parrish
[4] http://admin.indiaenvironmentportal.org.in/category/author/stohl-et-al
[5] http://admin.indiaenvironmentportal.org.in/category/journal/nature
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/ozone
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/atmosphere-and-ozone-layer
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/green-house-gases
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/asia
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/china
[12] http://admin.indiaenvironmentportal.org.in/category/thesaurus/n-c-america
[13] http://admin.indiaenvironmentportal.org.in/category/thesaurus/india