The 10 Primary Air Purifier Technologies (In Chronological Order):

1. Charcoal Filters (1854) – Absorbs odor and some gases.
Pros: Good for smoke, pet odor, and hazardous fumes. Inexpensive.
Cons: None.
2. Ozone (O2) (1881) – Ozone is what you might smell in the air after a thunderstorm. It’s oxygen with an extra charged particle attached which is unstable and only lasts a second but does a great job on odor, mold, etc.
Pros: It kills odors better than anything else. Kills mildew and mold. Good for chemical removal as well. (I love a little Ozone which I turn on a few hours before bed to make the room really fresh and clean)
Cons: In small amounts (low level) it is safe and very effective. (Consumer Reports blasted Sharper Image/Ionic Breeze because their unit put out very high levels of Ozone. As a result unfortunately many people are now afraid of ozone)
Note: Because of Sharper Image Manufacturers are now either 1) avoiding Ozone 2) calling it “Activated Oxygen” 3) putting timers on Ozone or 4) saying their units kill Ozone to capitalize on public perception (which overlooks the benefits). This is too bad. Ozone is excellent when used at low levels and there is little proof that it has harmed anyone. High levels are believed to inflame tissues.
3. HEPA (1934) – HEPA filters trap up to 99.97% of dust, pollen, dander, etc. Originally designed by the US Government and Military to protect soldiers and scientists from radiation it does offer some ability to remove any radiation in the air from Nuclear spills like those in Japan. Many manufacturers leave HEPA filters out of their air purifier because of the manufacturing expense.
Pros: Essential for allergies, dog/cat hair, pollen etc. A must for asthmatics.
Cons: HEPA filters have to be replaced, but they work very well. Replacement filters are typically overpriced (like printer cartridges) so look for a Purifier Brand whose replacement costs are reasonable (maybe $50-80 depending on the size/thickness).
4. UV Light (1936) – UV light kills many pathogens such as mold, viruses, germs and bacteria. (Used in hospitals) .
Pros: with today’s pathogens and bacteria strains UV is a great addition – especially if you have children, asthma, or immune challenges.
Cons: You have to replace the bulb(s) every year or so. Like with HEPA make sure the Manufacturer isn’t “soaking” you for high replacement costs. Don’t pay more than $20-30 for a bulb.
5. Negative Ion (1974)- Negative Ion is a positive thing for removing some pollen, smog, and some dust. The early ionizers would make your walls black because the charged dirt would adhere to the walls around the unit. That’s now taken care of by grid plates.
Pros: Very affordable method for cleaning the air.
Cons: It works well in combination with other technologies but it’s not very effective by itself. Often the air goes by too fast to kill all pathogens.
6. Ceramic – Uses heat inside a chamber to kill pathogens in the air as air is drawn into and thru the chamber. (This is also how a fever works in our body, raising the temperature to kill a virus).
Pros: Heat kills pathogens.
Cons: Most experts believe UV does a better job, with a lot less electricity. You don’t see many of these filters for that reason.
7. Washable Pre-Filters – This basically catches hair and large airborne particles. Most purifiers have these.
Pros: Very inexpensive addition by manufacturers. It also extends the life of the other filters.
Cons: None
8. Ti02 Photo-Catalytic (1991) – Enhances the UV light up to 4000% to kill germs, viruses, mold, bacteria, as it passes through the filter.
Pros: What’s great is now the UV bulb doesn’t have to be as strong or as big yet works more effectively.
Cons: None.
9. Plasma Dust (or Grid) Filters (1989) – Uses a charged grid plate to shower the incoming air with both positive and negative ions. Removes some airborne particles and some micro-organisms. I wouldn’t count on this alone but it will do some cleaning as you’ll see when the plates get dirty. It’s basically an ionizer on steroids. The “Never needs a replacement filter” types (Ionic Breeze, Oreck) fall into this category. (Note: You never need a replacement filter because your lungs are filtering what it doesn’t do a good job on)
Pros: You can wash it.
Cons: Works well, but needs other technologies to do a good job.
10. Water – There are now air purifiers which use water as their filter. Also water-based vacuum cleaners like the Rainbow and H20 Vacuum seen on TV infomercials. Water cleans the dust and dirt out of the air but is not effective for odor or any gas (chemicals, pollution). The water will also add moisture to the air – a potential mold/mildew enhancer. The water will need to be cleaned often to prevent mildew and bacteria being spread by it. Most water air purifiers cover a very limited area.

Pros: No filters to change. Will remove some dust and pollen into the water.
Cons: Extremely limited area of coverage. Inefficient use of energy. Adds mold potential to the room and air if not kept sanitary.
IN SUMMARY
Here’s how each of the 10  basic technologies work by category:
#1 HEPA, Pre-filter, Neg/Ion, Plasma Grid = Helpful for allergies and asthma, and some odors
#2 Carbon, Charcoal, Ozone, Zeolite = Helpful for odors, smoke, animal smells, chemical sensitivity, and protecting our immune system
#3 UV, TiO2, Plasma Grid, Ceramic = Helpful for immune system protection (colds, flu, viruses, pathogens), and eliminating musty odors