Most large urban areas tend to have only one air quality monitor for every 100 to 200 square miles.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/researchers-develop-new-hyper-local-air-pollution-map
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/zee-news
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-quality-monitoring
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-quality-standards