Quoth Wikipedia: Negative air ionization therapy (NAIs) uses air
ionisers as a non-pharmaceutical treatment for respiratory
disease, allergy, or stress-related health conditions. The mainstream scientific community considers many applications of NAIs to be pseudoscience. Many negative ion products release ozone, a chemical known to cause lung damage.
Coffee is mostly safe though. It can slightly weaken your bones though so if you have osteoporosis like I do you should avoid it.