I started to write a new library for the Air Quality sensor since the original code from the Seeedstudio page is very bad and buggy, e.g. using i as a public variable or initializing by a given pin (_pin) and then always read from pin 0 (A0). As well it is hard to understand what the intention was.
You can find the code on github MikeHg/AirQualitySensor (unfortunately I’m not allowed to copy the complete URL in this Forum - off-site URL, but I hope you find it).
Of course you are invited to contribute if you find it useful and want to improve it