AirDoctor's UltraHEPA Filter is 100 times more effective than ordinary HEPA filters, capturing 100% of some of the most dangerous ultra fine particles as small as .003 microns in size. The AirDoctor combines a proprietary dual action Carbon/Gas Trap/VOC Filter which removes dangerous ozone, gas and volatile organic compounds like formaldehyde. It circulates the air in a 638 square foot area at a rate of four times an hour, or in 1,274 square feet at a rate of twice an hour. AirDoctor's Auto-Mode uses a professional-grade air quality sensor to assess the air quality in the room and immediately adjust to the correct level of filtration.