Pollutants produced outdoors may penetrate into the indoor environment and may affect human health by exposure both indoors and outdoors. This is why it is important to control the air intake into a building. Also the use of openable windows needs to be considered in most polluted areas.
At the same time we have to take care of how the building effects its environment. It is important that the quality of exhaust air from building is clean enough. A special attention needs to be paid in densely populated areas.