Air cleaning is commonly used in industrial operations to reduce emissions of particulate dusts as well as gaseous and vapor-phase contaminants to the ambient atmosphere. It is also used as a contaminant control measure in indoor environments. Air cleaning is used both generically and to control specific contaminant problems. It is often used by individuals in an attempt to reduce exposure to allergens and other suspected indoor air contaminants. It is rarely used as a mitigation measure to resolve problem building complaints.