TRUTH: Most air purifiers have the function of turbo cleaning or quick cleaning. It is to supply maximum air flow with a highest fan speed.
Countering this, however, is an even stronger low pressure system created by the exhaust vent, because the air leaving the unit is forced out at a high velocity (high velocity creating low pressure). You can feel exhaust blowing hard onto your hand, but do not feel equally strong suction on the intake side of any fan.
As a result of these differences in velocity, much of the particles that theoretically move through the unit's filter bypass the intake and moves toward the exhaust vent instead. Ironically, we see an insidious effect when we increase the fan speed, expecting faster, better cleaning, but actually exacerbating the bypass problem through the creation of an even stronger low pressure system at the exhaust vent.
Literally harmful particles are attracted to the stronger exhaust side, forcing the filter to be bypassed ultimately recycling back into the air.