What is the source of air pollution data in the Weather app? I'm in Mexico, and today I looked at my phone and saw this:



It's the Weather app that came with iOS 13. Is there any way to find out what the specific pollutant is? If there is no way within the app, does anyone know where the data is from, so I can go find details?

There is an icon for the Weather Channel down in the bottom, so I went to that web site (weather.com) and searched for the city. I don't see any pollution data. 

I searched the web and found this: https://aqicn.org/. But they have no data for this particular city, so that's probably not the source either.
When I press the "The Weather Channel" logo a the bottom it takes me to a weather.com page that lists the air quality:



Then pressing on the "See Details" link shows the details about the air quality: