1/ Since I'm seeing a lot of misconceptions about air sensing, here's a thread to help clear up some of those misconceptions. For one, there's no consumer sensor or array of sensors out there that provide an accurate picture of air quality.
2/ In fact there's not great real time systems at any price level for sensing air quality. To get a true picture, you need lab equipment, and sometimes you have to wait to complete a whole lab method.
3/ Let's start with particles, since I've seen a lot of discussions on those lately. The most accurate particle counts come from gravimetric devices. Most consumer sensors though, work on a much simpler principle.