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Activated carbon is widely adopted by air purifier manufacturers for the removal of
gaseous pollutants. Activated carbon is essentially charcoal that has been treated
with oxygen to open millions of small pores between the carbon atoms.
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These pores adsorb harmful gases and odors. Due to the large surface area of the
carbon granules, carbon filters are excellent at trapping gases that pass through
traditional particle filters.
However, as the pores become filled with trapped contaminants,
the filters loose effectiveness and needs to be replaced.
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While activated carbon in its granular form is unquestionably effective for the removal of
many gaseous contaminants, most room air purifiers on the market today use carbon fiber
pads, which are only impregnated with activated carbon dust. These filter pads contain
only a few ounces of actual activated carbon and therefore ineffective
in removing gases and odors.
Choosing an Activated Carbon Air Purifier
 Quantity of activated carbon in the filter
Activated carbon works by adsorbing gaseous contaminants on it's surface.
Large amounts of carbon will last longer because it has a larger surface area for adsorption.
Also, depending on amounts of pollutants being adsorbed, a small amount of carbon can be
depleted within weeks making it useless.
The thickness of the activated carbon filter
A thicker the filter has a higher adsorption efficency because the gaseous pollutant
has to go through a long maze of activated carbon.
Impregnated carbon fiber pad or granular activated carbon?
Granular activated carbon is more effective than a 2" thick impregnated carbon pad because
it has a larger surface area for adsorption.
Also, the contact time the carbon has with
the gaseous pollutant is less in a pad, so it's adsorption rate will be lower. An
impregnated pad will also require more frequent change compared to a canister of
activated carbon.
Other things to note ...
Some manufacturers may claim that their activated carbon filter eliminates all
gaseous pollutants and odors - a feat that is scientifically impossible.
Specific gaseous contaminants need specific gas phase filtration technology.
While highly effective, activated carbon does not efficiently adsorp
low molecular weight gases. For this reason, special sorbents are needed to effectively deal
with other pollutants such as formaldehyde, hydrogen sulfide and ammonia.
Also, some unscrupulous manufacturers may use zeolite which is cheaper than activated carbon.
Zeolite is a natural mineral, whose pore structure is supposedly better suited for the
adsorption of gaseous compounds like formaldehyde and ammonia. However, there is no reliable
scientific evidence to show that zeolite is able to remove any gaseous compound
better than specialty impregnated carbons or impregnated alumina.
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