I'm making an air pollution-detecting device.
That sounds great but is hardly the point, and using a standard bluetooth terminal is good advice. You need to be able to walk before you can run. At the moment, you haven't the faintest idea of what you need to do to walk, and making an phone app has to be right at the bottom of the list of priorities. Using a standard terminal means you have something that works, at the moment the only thing, and enables you to address the real problem(s) - which you seem to be ignoring.