Here is one theory as to how NAI (negative air ions) might create effects within us. The title of the article is: Reactive Oxygen Species, by N. Goldstein. The radical called superoxide O2- has been recognized as a key signaling molecule, for mitochrondrial biogenesis*,and to stimulate production of SOD (superoxide dismutase). Air ions are small enough to be absorbed into the brain directly via nasal inhalation.
*See, “Mitochrondria an the Future of Medicine” by Lee Know, ND, published in 2018 and available as an ebook (Kindle).