When looking through air purifier reviews online, first verify if the air purifier you're looking at even has an activated carbon filter (many do not).
Activated carbon is the most effective and most widely used filtration media for removing airborne chemicals, gases and odors (the military first staring using it in gas masks in WWI). The power of activated carbon lies in its incredible microscopic porous structure that is capable of adsorbing and retaining toxic airborne pollutants.
The next thing to look for in an air purifier review is the actual depth of the carbon filter.
To be used efficiently in air purification, an activated carbon filter must offer an adequate amount of bed-depth to be able to significantly improve air quality. Many air purifiers claiming to offer chemical and odor filtration or air purification for tobacco smoke only provide a thin mesh-like filter impregnated with carbon dust. This type of filter doesn’t have enough carbon to effectively and consistently trap pollutants, as the pores would fill too quickly, often rendering the filter useless with days. (Think of a sponge: A thicker sponge can pick up much more water than a thin sponge!)
To maintain superior air quality levels, an activated carbon filter should offer in the range of 2” of depth like the AllerAir 5000 or AllerAir AirMedic +. This allows the pollutants to have a significant amount of dwell time in the filter, allowing more pollutants to be trapped on every pass. A deeper carbon filter also has a much longer filter life, lowering overall maintenance costs and providing on average, almost 9000 hours of clean air*
*Based on the average carbon filter life of two years in a typical residential setting. Environments in which chemical and odors are at increased levels may require more frequent filter changes.