The Winix A231 air purifier features a 360 all-in-one 4-stage air purification system, this unit removes 99.97% of airborne particles as small as 0.3 microns in size. Winix s PlasmaWave Technology may help to reduce the presence of airborne pollutants, allergens, and impurities. The unit s built-in Smart Sensor detect and monitor the quality of air in your environment and provides a visual representation of your current air quality. When in Auto Mode, the unit automatically adjusts fan speeds to ensure efficient and cost-effective cleaning. Activate Sleep mode for quiet, energy-efficient operation.