Activated carbon has been specially treated to open up millions of tiny pores and fissures. This creates a huge internal surface area. In fact, less than a handful of carbon has the surface area of an entire football field. When polluted air is drawn into the air purifier, chemicals, gases and odors are trapped in these openings. An air purifier made specifically for chemicals and odors will have a thick filter of granular activated carbon. Avoid any air purifier that uses only a thin carbon filter. This type of air purifier simply does not have enough carbon to be effective. It will quickly become saturated and may stop adsorbing within weeks or even days. A large carbon filter could last up to two years depending on the level of odors and chemicals in the dwelling.