your body has a good purifier called nostril hair, ciliary tract and then mucus lining your lungs... the body expels or clears dirt away from the air breathed in... naturally
if you constantly cough or nose is irritated, your body is telling you your environment is not clean... then perhaps can consider...
but perhaps maybe just find out the source and remove it ... or grow plants to act as natural purifiers too.
same for humidity... air too dry not good for skin... too humid... you will first notice your room has mould... furniture decaying.... if not... aircon can also clear away excess humidity too