I would seriously doubt any airline would allow the use of an air purifier inflight. Some devices such as Portable Oxygen Concentrators can be used under strict circumstances (such as the model has been approved, is battery powered, pax has sufficient batteries for the flight duration plus diversion time etc). Look at your airline's web-site for details. (Search POC + your airline).
99.9% of airplanes in the western world use HEPA filters which are likely to be much better than any commercial air purifier that you can find. The air is re-circulated every few minutes.
You won't be able to use the purifier in the queues for check-in, baggage drop, security, at the gate, etc. You are much more likely to catch a bug in these places than on the airplane.
Get disposable masks from the pharmacy and wear them, if you are really concerned.