Air ions

Ions are formed from originally neutral particles that have been positively or negatively charged by ionization. These charged particles are very small, have high mobility and can be spread quickly by the wind. Due to their electrical charge, these particles tend to form clusters and combine with larger particles and aerosols in the air. The cleaner the ambient air, the longer the ions are present as small ions, floating in the air to be deeply inhaled by breathing. High levels of air pollution quickly lead to the formation of larger ions with less positive health effects, as they sink to the ground more quickly and can also be inhaled less deeply. Light air ions, which usually consist of negatively charged oxygen molecules and have a beneficial effect in particularly high concentrations, are thus particularly healthy for humans.

Because plants are important producers of negative ions, the concentration of negative air ions in cities is significantly lower, at 100 to 800 ions/cm³, compared to green areas and forests where the concentration is around 700 to 2,000 ions/cm³. The ions are formed during photosynthesis: the more intense the light source, the more negative air ions are formed. The number of negatively charged particles therefore increases with increasing altitude, as the solar radiation becomes more intense. The concentration of negative air ions is highest in natural environments that host a water source, such as a river or waterfall. The air ions are created by the unbridled force of flowing water, breaking waves or especially by the force of falling water, as is the case with waterfalls, the main producers of negative ions.

Studies of medical evidence:

• Indication: respiratory function (Alexander, Bailey, Perez, Mitchell & Su, 2013): evidence level Ib
• Indication: anxiety, mood, relaxation, sleep; depression (Perez, Alexander & Bailey, 2012): evidence level Ia
  

A range of single studies suggests that negative air ions have multiple health benefits on humans. They have a clear influence on human health and well-being. A positive health effect of negatively charged air ions seems to be apparent as regards immunological, physiological and psychological aspects. However, some of these results need to be further verified in high quality studies. 

In combination with water aerosol from e.g. waterfalls they are likely to induce an immune-modulatory effect (see also Waterfalls).