You may be surprised that only approximately 25 percent of indoor pollutants are traced to outdoor sources. The majority of materials circulating in your home and settling in your ducts are from indoor products. Cooking sprays and ingredients are significant contributors to indoor air pollution. As solid particles come into contact with cooking emissions, a somewhat greasy layer of material may develop on your coils and in your ducts. The airstream alone won’t remove such material, and air duct cleaning methods may be required.