Activated Carbon in Home and Room Air Purifiers

I. Introduction
The presence of activated carbon in room air purifiers may be a mystery to you, unless you're a aquarium hobbyist, or own a water purification system which uses carbon. For many people, the first time they encounter it is in selecting home air purifiers. Although most of our customers begin their search because of allergies or asthma, many soon realize how much odors and the chemicals with can cause them also contribute to their respiratory problems. That's why most quality room air purifier systems also address these issues.

II. History and Use in Purification Processes
As many as 2000 years ago, human beings were using activated carbon to remove impurities from water. Even then it's exceptional adsorption qualities were known. However, it was not until the early 1900's that it was produced in a form (as powder) that could be sold commercially. At that time it was used to purify water (so that it had no smell or taster) and to take the color out of sugar. As World War I got into swing it was discovered that it could be used in gas masks to protect soldiers, as well as for war time water and air purifiers. Instead of being used in powder form, granular activated carbon was developed. From that point on, activated carbon was used in many ways.

III. Why Is It Called "Activated"?
If you are unfamiliar with activated carbon and wonder why it is called "activated" and if there is such a thing as non-activated carbon, this will solve the mystery. The heat used in making carbon "activated" drives out impurities so there are places for impurities from your air to reside when it is used in an air purifier. After activated carbon is used for a while, it can actually be reactivated by cooking it again. However, this is impractical and dangerous. "Non-activated" carbon is soot or charcoal.

Activated carbon is described in a variety of ways, and there are a variety of types,  but generally it includes a wide range of amorphous carbon-based materials which exhibit a high degree of porosity and an extended surface area. In simple terms, this means that it has excellent absorbent characteristics that make it very useful for a wide variety of filtration processes including air and water.  

IV. How Is Activated Carbon Used in Home Air Purifiers?
In room air purifiers, the activated carbon is often combined with other minerals like zeolite.  Zeolite can absorb ions and molecules and thus act as a filter for odor control, toxin removal and as a chemical sieve. In some units, the carbon may be impregnated with a potassium iodide or blended with impregnated active alumina to increase the absorbent qualities. These home air purifiers are particularly helpful to people with Multiple Chemical Sensitivity (MCS), because they absorb formaldehyde which is found in carpet, wood paneling, and furniture upholstery. Perfumes as well as chemicals in household cleaning items are also removed, making the environment much more breathable for people in general, but especially asthma sufferers, babies, children, and the elderly.

V. The Carbon in Room Air Purifiers
The type and amount of activated carbon, other materials with which it is blended, and how it is used in home air purifiers depends on the brand and model. Here are the highlights:
Austin Air HM400 – contains 18 pounds of granular activated carbon impregnated with zeolite to enhance chemical adsorption.
Austin Air HM400 SuperBlend (also called Plus) – contains 18 pounds of granular activated carbon impregnated with a blend of zeolite and potassium to make it effective at removing formaldehyde.
Blueair 501 or 601 - the Blueair system contains three integrated HEPA/carbon filters. Blueair does not publish a weight for the carbon included. The optional SmokeStop filters have substantially more activated carbon than the standard filters that come with the unit.
IQAir HealthPro Plus – The V-5 Cell filter in the IQAir HealthPro Plus has a five filtration chamber which includes a blend of activated carbon and impregnated active alumina for enhanced adsorption. IQAir does not publish the weight of the activated carbon included.

VI. Summary - Home Air Purifiers
For many people, particulates such as pollens or pet dander are the main irritants, with odor and chemical adsorption being less important or not important at all. For others who need a high degree of both, it is best to look at the higher caliber room air purifiers which offer outstanding particle, odor and chemical removal. VOC's (volatile organic compounds), smog, ozone, fumes from cooking, pets, or tobacco can be unhealthy or irritating for anyone not just allergenics and asthmatics. If you're going to have home air purifiers anyway, it only makes sense to get some that can absorb practically everything.

Ted Zajac, Jr.
MSE Johns Hopkins University