An air purifier is a device that can clean the air you breathe. The air purifier does not cool the room like an air conditioner, but only to release fresh air that is clean or pollution-free.An air purifier or air cleaner is a device that removes contaminants from the air in the room to improve indoor air quality. This tool is usually marketed because it is useful for people with allergies and asthma, and to reduce or eliminate secondhand smoke.