Build your own inexpensive sensor, contribute to the global network. See also https://github.com/opendata-stuttgart
I should try to script at least my systems so they write into as many of the open networks as I can manage.
The inexpensive part makes citizen science viable in sub-economic and hobbyist settings.
https://openaq.org/ is trying to consolidate air quality data, but I'm uncertain of their licensing and goals.
I was expecting China and India to be dark purple
...you simply select the English firmware `latest_en.bin`. Or one of the languages you prefer.