Take a look on iGAS internet gas monitor from Turnkey. https://www.geonoise.com/igas-air-pollution-monitor/

It really depends on what you want to learn. Many CO sensors won't tell you very much except for a case where there's a large source inside a building, for example.

Here's another option: https://www.aeroqual.com/indoor-air-quality-monitors/indoor-air-quality-sensors