If you click on the dots, it takes you to a city: https://air.plumelabs.com/Dallas https://air.plumelabs.com/Dallas https://air.plumelabs.com/London https://a

If you click on the dots, it takes you to a city: https://air.plumelabs.com/Dallas https://air.plumelabs.com/Dallas https://air.plumelabs.com/London https://air.plumelabs.com/London https://air.plumelabs.com/Bogota https://air.plumelabs.com/Bogota https://air.plumelabs.com/Beijing https://air.plumelabs.com/Beijing https://air.plumelabs.com/New-Delhi https://air.plumelabs.com/New-Delhi https://plumelabs.files.wordpress.com/2015/12/world-air-map-live.gif https://plumelabs.files.wordpress.com/2015/12/world-air-map-... The unit/metric descibed by each graph seems to be: The Plume Air Quality Index™ I'm not sure how the index value is determined, but it seems to factor in measured values for Nitrogen Dioxide, Ozone, Carbon Monoxide, and particulate matter (exhaust soot and toxic dust being worse than dust comprised of ambient organic material such as pollen).