AirDoctor features a built-in ionizer that is off by default. The ionizer revitalizes the air by infusing it with negative ions, much like the effects experienced after a rainstorm or while living by the sea. Some people appreciate this effect, but using it is completely optional.
Additionally, the negative ions attach to particles, giving the particles an electrical charge that causes them to clump together and allows them to be more easily captured by AirDoctor.
AirDoctor functions perfectly well even if you never opt for the ionizer feature. It does not rely on the ionizer to achieve its high level of 0.003-micron air purification.