All air purifiers use an electric motor powered by altering current to turn a fan and move the clean air.  An electronic board regulates the power that is appalling to the fan speed, and it provides different fan speeds. They both generate EMF radiation, which is terrible for your health.
But, most air purifiers have standard altering current power connected with an electronic motor and a fan speed switch. The AC is low-frequency, modified by a pulse width modulation board that controls how voltage is appalling to the motor. So this type of motor is better since it emits low EMFs.