A "negative Ion" is nothing more than a molecule of anything floating around with an extra electron riding along for free. Somebody once decided that the electrical charge of an electron was to be called negative -- so a molecule with an extra electron is called a "negative ion".
There are three things that happen with this negative ion that are of interest to us:
* When this little ion bumps into something bigger, such as a piece of pollution (dust, pollen, even radon gas) it tends to drop off that free-loading electron onto the other particle. Now, since the walls and floors of your house are usually positively charged, they will attract this piece of pollution and stick it to the wall or rug -- that is called precipitation. You may not like your walls getting dirty faster, but your lungs stay cleaner longer.
* When the negative ion dumps its free-loading electron onto an airborne virus (like a cold or flu bug), the electrical impulse triggers the virus into coming out of its protective shell, only to find itself hanging in the air, where it quickly dies. The virus can only survive if it emerges from its shell directly onto moist body tissue. A more recent description of its action on airborne microbes and viruses (2019) is that the extra electrons deactivate the proteins that encase the virus. In 2020 it has been found to be effective against Covid-19 along the same lines as UV light.
* In a yet poorly understood way, the human nervous system functions by electrical impulses and our entire biological system is tied into electrical currents within and around our bodies. Hence, the science of electro-environmentalism and electro-bio-chemistry. Negative ions exist abundantly in the natural outdoor air and are our major source of free electrons: the air we breath carries these negative ions into our lungs, where the electrons hop off onto our highly conductive internal body tissue. Long before science began to seriously study these things, people in Europe and Japan began to observe that when you put humans into environments that have no source of free electrons (no negative ions) they began to have biological and psychological problems ranging from breathing difficulties to headaches to sluggishness and to depression.
In short: Negative ions clean airborne pollutants from the air, kill airborne germs, and supply the human body with necessary free electrons.
Negative ion generators are machines that electronically create negative ions identical to those found abundantly in country and mountain air. Some companies have produced inferior negative ion generators that produce corrosive ozone as a by-product. Negative ions should not be confused with ozone molecules, which are corrosive oxygen derivatives. (Ozone generators should only be used under a doctor's instruction and Health Canada has issued warnings against their use in homes.) No harmful effects have ever been attributed to high doses of negative ions -- the body just ignores the surplus electrons, even pushes them away when it begins to become negatively charged. "Corona discharge" is the only reliable method to date to generate negative ions without significant quantities of ozone as a by-product.
My tested recommendations
Bionaire makes several air filter systems that include good negative ion generators; Electro-Air Five Seasons filter systems tend to have even more powerful negative ion generators. Global Plasma Solutions (GPS) has developed a patented totally ozone free system generally made for large systems for offices and commercial building since 2009 with some small units as well for residential use, but the 2020 Covid demand has outstripped supply for the small residential units. A visit to their website will give you a whole series of videos showing what I have explained above.
The story continues with Why Should I Care About Negaive Ions.