Abstract: An apparatus and a method for spraying a starting solution into a gaseous medium under certain conditions. The method includes the steps of a) supplying the starting solution by delivering means using a pump to spray head members and spraying the starting solution through the spray head members, each spray head member having a plurality of holes for producing droplets of substantially constant radius substantially independent of spray head operating pressure, and b) washing the spray head members connected to at least one starting solution supply conduit substantially at its surface and purging them from foreign material with starting solution in the supply conduit.