[yagurastation]

Unfortunately, yes, the space is fragmented. A long while ago I chose https://luftdaten.info/en/ because sensor firmware, DB, and tools are truly open source (GPL, ODbL, MIT). Next to supporting many sensors, it also allows for your own back-ends (API, InfluxDB). The community is awesome and has hacker values.

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.