WHAT ARE INDOOR AIR POLLUTANTS? Indoor air quality generally decreases due to internal and external pollution factors, and inhalation becomes dangerous. Outdoor pollution sources can include busy streets, bus terminals, parking lots adjacent to buildings, train stations, airports, manufacturing, industry, agricultural areas, and more. Outdoor pollutants affect indoor air quality. Also, unmaintained air conditioning systems, office, construction materials, photocopiers, laser printers, detergent and cleaning materials, sprays, and cigarette smoke turn into particulate and gaseous pollutants indoors.