Yes. While most pollutants affecting indoor air quality come from inside the building, some may originate outdoors. According to the EPA, outdoor air pollutants can enter the building through open doors, windows, ventilation systems, and cracks in structures. Harmful smoke from chimneys can also re-enter the home and pollute the air in the home and neighborhood. Chemicals in water supplies can enter the home when occupants are using water, such as when showering or cooking.