There are 10 types of air purifiers:

1) HEPA
2) Ionic (also called ionizer or electrostatic)
3) UV
4) Tio2
5) Pre-Filter
6) Carbon
7) Zeolite
Water
9) Negative Ion
10) Ozone

Here are several short videos on the pros and cons of each technology…

#1 HEPA Air Filters…

#2 Ionic Air Purifiers… (also called ionizer or electrostatic)

3) UV

4) Tio2
5) Pre-Filter
6) Carbon
7) Zeolite
Water
9) Negative Ion
10) Ozone