Does air travelling via a simple fan (no ionizer) through an electrostatic filter (like Filtrete) get ionized?

Joe: I think you have ionization and ozone confused. Most all ionizers create ozone as a byproduct. Especially the ones that use corona discharge. Ions are just electric charges. They can be positive or negative. They are not free radicals. Ozone is 3 oxygen molecules together. Because oxygen is unstable, it does not occur in nature in one molecule. That one molecule always sticks to something else. The air floating around you (inside and out) is what we call "oxygen" but it is really 2 oxygen molecules bound together. With ozone, that third particle can break away and serve as a powerful oxidizer. Now that is where your get your free radical. If it is not an occupied space, that ozone can be a powerful air cleaning agent. It is commonly used in fire restoration to remove the smoke odors. Great for things like that but not so great to have running in the house all the time. The ozone can be a respiratory irritant and trigger asthma.
Now, the electrostatic pleated filter like filtrete is doing something completely else. The filtering material is chosen because it is highly prone to static electricity. What happens is the flow of air through the material creates friction. This friction results in the build up of static electricity. Just like when you wear socks and rub them on the carpet in the winter. The amount of charge built up will depend on the relative humidity of the air and the rate of flow of the air. As the charge builds up, it causes airborne particles to stick better to the filter. Of course, when the airflow stops, you lose your electrostatic charge, but most manufacturers these days use some type of coating to make the material tacky so the captured particles stay put. Also, if you want maximum air filtering area for your filter size, make sure you get a pleated filter. There is more filtering area in a pleated filter that is 20 x 20 than there is in any flat filter that is 20 x 20. So, don’t be afraid of ions. Do be aware of ozone, and don’t worry that your electrostatic filter is going to make ozone. (BTW – negative ions make you feel good and positive ions make you feel bad…how is that for backwards?)