I tried with all available libraries. The results were always the same - far away from the truth.
The CO sensors that I use are model ZE07-CO, produced by Winsen. I am very happy with that sensors. They are very accurate.
If you have an interest, please send me an e-mail to vcoder(@)abv.bg, and I will explain you what sensors and software I use in my fire and health safety alarm system in my house (I do not want to spam the theme here 
)
BR