Ionization of the air is simply “the insertion of ions in the air.” An ion is an electrically charged atom or molecule, and can be positive or negative. These ions can react with the molecules present in the air. This is usually accomplished through the application of high voltage whereby electrons may be released or captured. In addition to the generation of a current, or the creation of a potential difference, the use of plasma or an ultraviolet radiation source may also be used .
There may then arise positive and negative ions. These ions can react with other molecules, for example, oxygen. In addition, they cause solid particles in the air to bind together, causing clustering of these particles thereby forming larger particles which then fall to the ground. Various vender websites often referred to the production of negative ions in nature. For example, air ionization by lightning in a summer thunderstorm.
Due to the large discharge the air fills with ions after which we often experience tingling smell and an upgraded air cleared. A less well-known fact is the formation of ions in a waterfall. A waterfall continuously modifies the ion spectrum above. According to Lutz, the type of ions significantly changes as we move further away from the waterfall. Ions are formed by, among other things, a combination of ions caused by auto-ionization, rapidly moving water causing the collision of molecules and the evaporation of water droplets [5, 6].
Ions in the air may be created in various ways. With the aid of alpha particles (helium nuclei), or by generating an electric field via a corona or plasma. One of the most innovative methods is based on the use of a semiconductor technology (SPD) combined with a lighting lamps .
Generating ions with alpha particles often works on the basis of a radioactive source (Po-210) . This happens when He-nuclei collide with air molecules, causing electrons to be emitted. When alpha particles are ionized in this way, they form both positive and negative particles. Each particle which loses an electron becomes positive, and each particle which receives an electron becomes negative. A major disadvantage is the required radioactive source (in our example Polonium). Even stronger radiation sources, such as gamma radiation from a Cobalt 60 source, can generate ions which cause a reaction with air producing negative ions. It is self-evident that such a method is not acceptable for indoor use.
Another way to generate negative ions is photocatalysis. NASA developed and used such methods to control the indoor air quality in space stations . Photocatalysis is nothing other than the acceleration of a chemical reaction under the presence of a catalyst and light. This method is based on a combination of titanium dioxide (TiO ) and UV light. . As a result, radicals are formed which can degrade organic molecules. The final degradation of organic compounds, for example, takes place at the surface of the material. Despite the fact that in this method negative ions play a role in purifying the air, the principle is completely different from the methods in which negative ions are generated by electricity.
If an electric field is initiated, for example by a corona ionizer, then these fields can repel or receive electrons. This depends on the charge of the ionizer. Positive ions move more slowly in the air than negative ions. The generation of positive ions requires higher voltage than is needed for the generation of negative [ao 9, 10]. By far, most commercial devices (mobile ionizers) are designed to generate negative ions, irrespective of whether they employ a corona, plasma, or semi-conductor technology. This semiconductor technique is a particular innovation in the field of negative ion production. Especially, as introduced by the company FreshLight. They have demonstrated, by a small device, a very efficient method of producing negative ions and illumination from the same lamp. . The following sections provide more detail on how negative ions are formed and what role they play in the indoor air.