Abstract: There is described a method for controlling the amount of ionized gases and/or particles suspended in the air above roads, streets, open spaces or the like. This is done by establishing an electrical field between the top layer of a road, street, open space or the like, and the said ionized gases and/or particles. By means of controlling the electrical field we will be able to control the amount of ionized gases and/or particles. The invention also indicates how the electrical field can be established between surfaces in the immediate vicinity of a road, street, open space or the like, for example in tunnel walls. The electrical field is established by making at least the top layer of the surface concerned electrically conductive and connecting it to earth or to one pole of an electrical voltage source.