Ionization is the process whereby atoms and molecules become electrically charged, forming ions. An atom can gain one or more electrons to form a negative ion or lose electrons to form a positive ion. Air ionization refers to the ionization of air molecules. This can take place as a result of various natural processes, or a device can be employed to ionize the air in order to bring health benefits either directly or through air purification by the removal of airborne allergens, pathogens and pollutants. It generally is agreed that negative ions are more effective than positive ions for these purposes.
Air ionizers generally work by applying a high-voltage electric current to a metal prong or needle. An electric current consists of a flow of negatively charged electrons. As the electrons approach the end of the needle, the electrostatic repulsion between them causes them to detach from the metal surface and attach themselves to molecules of nitrogen and oxygen in the air and to airborne particles, forming negative ions.
Although the claimed direct health benefits of negative ions, such as relief from seasonal affective disorder (SAD) and depression, are the subject of research and debate, there is good evidence from a number of studies that ionization, particularly with negative ions, can purify the air by removing small suspended particles that might harbor harmful bacteria or allergens. It seems that when these particles become ionized, they tend to settle onto grounded surfaces, such as walls and floors, leaving the air cleaner. Air ionization has been used successfully in the dusty atmosphere of poultry farms, for example, to remove harmful bacteria from the air and to reduce the incidence of disease.
Another useful application for air ionizers is in the prevention of electrostatic discharge. For example, an electrical charge can build up on sensitive electronic parts during handling or assembly, resulting in sparks that cause damage. An air ionizer can help neutralize charges before discharge takes place.
The effects of air ionizers might not always be beneficial. The ionization of nitrogen and oxygen can result in the formation of small amounts of ozone and nitrogen oxides. These are lung irritants and are classed as pollutants. There is concern that some air ionizers could generate harmful levels of these gases.
Air ionization can also take place naturally, such as during thunderstorms and by the action of sunlight. Rock that is subjected to pressure can generate electric currents that might manifest themselves as air ionization around surface rocks. It has been suggested that earthquakes could be predicted by the detection of ionization effects in earthquake zones.