Residential air purifiers and air cleaners are machines that remove airborne contaminants including dust, smoke, pollen, and pet dander to enhance the quality of the air indoors. The primary part of a home air purifier is the high-efficiency air filter. Residential air purifiers come in two primary categories: stand-alone and in-duct. Stand-alone, as the name implies, is a portable room system made to purify and cleanse the air in a specific room at home or work.