What is the difference between a Host, Sponsor and Contributor?

A Host sets up and maintains air quality station(s). You can receive remote on onsite training to install the station.
A Sponsor has generously provided funding to obtain, install and maintain sensor(s) for period of time.
A Contributor serves as both a Host and a Sponsor, who not only obtains sensor(s), but also maintains the sensor(s).

See more information from the following: Air Quality Community | IQAir