Awair produces several indoor air quality monitors that measure temperature, humidity, carbon dioxide, dust (PM2.5), and VOCs, accessible via mobile app: Awair, a tabletop model, Awair Baby, similar to Awair but the casing has been replaced with a copolymer, and Awair Glow, which plugs into an outlet and can power on “non-smart” devices like air purifiers when air quality drops.
Netatmo makes several indoor and outdoor air quality monitors. Their Smart Indoor Air Quality Monitor measures humidity, air quality, noise, and temperature, and comes with a companion smartphone app. An API is available.