Hi, as a part of my project, I am working on an air quality monitor and a flammable gas detector. I have done a bit of research before selecting the sensors. After going through a lot of tutorials and articles, I used this Types of gas sensors article as a reference and thought of using the MQ series sensors for the project. The main positives I see in them are that they are cheap and will fit in my budget, and there are a ton of tutorials for these sensors. But, my question is, are they reliable? Do I go with them or should I choose some other sensor? Is the preheating period of 24 hours necessary? It would be really helpful if someone could point me in the right direction.

 

Here we are and a month and a half later I am the first responder to the question.
"Air quality" is a vast category that includes standards set by folks detached from reality.
So the very first request is to ask about what you are looking for. Toxic gases, carbon dioxide concentration? cigarett smoke? excess humidity? explosive vapors? or something else?
There are a huge number of products covering the whole realm, so a narrower range will help.

I have used the "Figaro" brand of semiconductor sensors once and they do require an initialization period, and an hour warm up tim after that. They perform as claimed.