Kinda sounds like a fools errand... I understand the desire to fly for a "good reason". But you would need to accomplish so many things just to get X sample at X altitude. If you wish to prove that air quality changes with altitude climb i hill or a building. Part of science is doing experiments without conjuring the ghost of Rube Goldberg.

On the other hand RC models is all about doing things in the name futility and pointlessly wasting time. So you need a clever way to fuse them together. Really it's like building a model with hot glue (you only create the illusion of a completed model).

I would suggest you use the model to create an aerial survey map and do air quality testing at various points of your image/map to show local variations at a constant altitude based on environmental differences of the location.