[amanfredi]

HEPA is only for particulate contaminants. At least some of the expensive filters have activated charcoal and other chemical filters.

[hcarvalhoalves]

> At least some of the expensive filters have activated charcoal

Activated carbon is effective just to remove odors and nothing more. It's not expensive either, it's like $ 10/kg retail.

A high-end filter is more likely to work with ionization. [1]

[1] http://www.amazon.com/Sharp-FPA80UW-Plasmacluster-Purifier-F...