How do air ions decrease?

Air ions decrease by: (1) Electronic neutralization Positive and negative air ions combine together and they are electrically cancelled out. (2) Diffusion Air ions tend to spread out to have uniform density. (i.e. higher to lower density) Generally, diffusion speeds of small negative ions are higher than positive ions. This means negative ions vanish more rapidly (i.e. shorter life span). (3) Absorption A tiny particle (e.g. dust, steam) lowers ion density and mobility when it absorbs an air ion. Absorption speeds are determined by diffusion speeds, therefore mobility of the ion. Generally, negative ions are more likely to be absorbed because of higher mobility values than positive ions. (4) Electric fields An air ion moves according to the electric field. However, it is said that it does not affect the movement much except under extraordinary events. (e.g. when thunder occurs.) The industry's highest performance negative ion generator (ionizer) [Users testimonials] Good sleep 74%, Alleviation of migraine 85%, Less shoulder pain 66%, Feel refreshed 76%