IQ.Airvisual
https://www.airvisual.com/ or https://www.iqair.com/
https://play.google.com/store/apps/details?id=com.airvisual
https://itunes.apple.com/us/app/airvisual-real-time-forecast/id1048912974?ls=1&mt=8%27
World's Air Pollution: Real-time Air Quality Index
https://waqi.info/#/c/49.214/16.501/11.7z
NY Times
https://www.nytimes.com/interactive/2019/12/02/climate/air-pollution-compare-ar-ul.html
#pm25