Activated Carbon What is a Carbon Filter?


NEWS: 08/07/04: Studies performed through Syracuse Center of Excellence in Environmental and Energy Systems.

Researchers found that currently available air cleaners employ a range of technologies, including sorption filtration (Carbon), photocatalytic oxidation, ozone oxidation and air ionization. None of the air cleaners tested was effective in removing all 16 VOCs in the test "cocktail". VOCs in the test "cocktail" included formaldehyde, toluene, perchlorethylene and methyl ethyl ketone, each of which is regarded by the U.S. Environmental Protection Agency as a "hazardous air pollutant" and all of which are commonly found in indoor air. Among the different technologies, sorption filtration using activated carbon or other materials was found to be more effective than other approaches in currently available air cleaners. "This study was designed to evaluate how well existing off-the-shelf technologies remove VOCs from indoor air." "Air purification is one of the key approaches for improving indoor air quality, together with controlling sources of contaminants and ventilating with clean outside air.


Before we explain Activated Carbon to you we first want you to understand how Carbon works with odors, gases and vapors. Many sellers of air cleaners with carbon in them simply DO NOT know how Carbon works and INCORRECTLY explain it. Once you understand HOW carbon works you will understand why MORE carbon is better and WHY those thin carbon pads on many cheap air cleaning units are useless.

What is Ab sorption and Ad sorption?

Many times we see the statement: "Activated Carbon ab sorbs airborne odors and vapors."This is not a true statement. A true statement is: "Activated carbon ad sorbs airborne odors and vapors." Do you see the difference? The word ad sorbis important here. When a material ad sorbs something, it means that it attaches to it by chemical attraction. The huge surface area of activated carbon gives it countless bonding sites. When odors and vapors pass next to the activated carbon surface, they attach to the surface of the carbon. They are added to the surface of the carbon, they are not absorbed by the carbon. They are ad sorbed. To be absorbed by carbon the odors and vapors would have to be diffused into the carbon, not simply attached to it's surface. Carbon DOES NOT absorb, it ad sorbs!

Here is a good example of the difference between the words "ABsorb" and "ADsorb":

If you have a cake and eat and swallow it, you are AB sorbing it. If someone throws a cake in your face, your face AD sorbed it!

Here is another one: If you use a sponge on your counter to clean up spilled milk and cookies, the milk is AB sorbed into the sponge. The cookie crums are AD sorbed to the outside of the sponge!

So, in air cleaning with carbon you NEVER ABSORB anything into the carbon. You ADSORB it onto the surface of the carbon!


Carbon is the most adsorbent material known to man and has been used to purify air and water for thousands of years. In fact, the use of carbon dates so far back into history that its exact origin has been impossible to document. Historians do know that as far back as 1500 BC the ancient Egyptians were using carbon to adsorb odors from festering wounds and from within the intestinal tract or to purify their water and that carbon filters were used for ventilating vapors and gases from 17th century London sewers. However it was the 20th century that saw the development of specially ';activated'; granular carbon. With the introduction of poisonous gases during WW I, the military developed large scale production methods for adsorbent carbons suitable for use in gas-masks, which has led to a post-war expansion in commercial production and applications of this amazingly versatile substance.

What is Activated Carbon?

Many natural substances are used as the base material for producing carbon. The most common base materials used are wood, coal and coconut shell. These base materials are subjected to a process called carbonization. Carbonization is a heating process where by the base material is subjected to high temperature which drives out any volatiles. To activate the carbon it is subjected to a second heat and steam treatment. The activation of the carbon is what gives it it's unique adsorption characteristics. The activation of the carbon creates carbon which is highly porous providing a large surface area of the carbon for adsorption.

Carbon that is ';activated'; undergoes a process which opens up millions of tiny pores and fissures to enhance the material';s adsorbent properties. The process creates a very large internal surface area, which is key to the power of activated carbon - the more surface area - the more the carbon can adsorb. Interesting to note that only 1 lb of activated carbon has typically a surface area of 125 acres or 200 linear miles of fissures. Due to the large internal surface area of activated carbons it can actually adsorb up to 60% of its weight. Good carbon filters of 10 lbs. or more, depending on the environment in which they are used, can last anywhere from 2 up to 5 years before all of the pores are full.

Are ALL Activated Carbon filters the same?

NO! Activated carbon can be enhanced and impregnated and/or custom blended to be a more specialized adsorbant. For an example: Using standard Activated Carbon (such as used for common household odors) is NOT effective in a Beauty Salon where ammonia and formaldehyde fumes are. The Activated Carbon for a Beauty Salon would be enhanced for those specific pollutants found in a Beauty Salon.

Does it matter how much activated carbon there is?

YES!Activated carbon adsorbs to it's surface. When there is no more surface left to adsorb to the carbon it is depleted of it's capability to be effective. Large amounts of carbon will last longer then small amounts because it has larger amounts of 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.

Does it matter how thick an activated Carbon filter is?

YES! The more contact time the activated carbon has with a pollutant, the better chances of it adsorbing it. The thicker the carbon filter the better it's adsorption. If the pollutant has to go through a long maze of activated carbon it's chances are also greater of being adsorbed.

Which is more effective, a pad impregnated with carbon or granular activated carbon?

Granular Activated Carbon is more effective then a 1" or 2" thick impregnated carbon pad. Granular activated carbon will have much more surface area for adsorption than a impregnated pad. Also, an impregnated pad will have to be changed much for frequently then a canister of activated carbon. Keep in mind that the contact time the carbon has with a pollutant is less in a pad so it's adsorption rate is also less.

Does activated carbon work the same way in Water Filters?

YES! Carbon works the same way in water as in air, ADSORPTION! Carbon water filters main purpose is to reduce or eliminate bad tastes and odors. They can also eliminate or reduce chlorine, and many organic contaminants in municipal water supplies, resulting in improved drinking water.

Replacement Carbon Media

After the activated carbon has adsorbed all it can is there a way I can re-activate it at home?

In order to re-activate activated-carbon, it must undergo a process called Pyrolysis. (The thermal decomposition of organic material through the application of heat in the absence of oxygen.). To fully re-activate saturated activated-carbon, you must heat it to approximately 1,472 °F, in a controlled atmosphere of low oxygen concentration to reduce the possibility of combustion. This fact is even stated in the U.S. Army Corps of Engineers - Engineering and Design, Adsorption Design Guide, Design Guide No. DG1110-1-2.

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