The OpenAQ Community harmonizes disparate air quality data from across the world so that citizens and organizations can fight air inequality more efficiently. The data is captured from multiple sources and made accessible to all through our open-source platform.

Bulk upload: https://upload.openaq.org/

An air quality monitoring network built on a new generation of Internet of Things sensors. Using a new generation of laser particle counters to provide real-time measurement of PM1.0, PM2.5 and PM10. PurpleAir sensors are easy to install and only require a power outlet and WiFi. They use WiFi to report in real time to the PurpleAir map. Sells air quality sensors that are pretty expensive. Don't know if it'd be possible to upload data from other kinds of sensors.

Account creation requires authenticating with a Google account only.

They have a JSON API but it's read-only and just a straight dump from their database: https://www.purpleair.com/json

https://www2.purpleair.com/community/faq#hc-access-the-json

There is also a Thingspeak API: https://www2.purpleair.com/community/faq#hc-thingspeak-api

They also seem to have a REST API but you need an API key and ChannelID. Not a big deal, really.

I don't know if this service is suitable for my purposes.

CanAirIO is a citizen science project using mobile and static sensors
to measure air quality with cell phones and low-cost technology.

A crowdsourced open environmental data project. volunteer centered. Measures airquality, radiation, and environmental health.