How may a Do-It-Yourself plant air filter incorporate the three air-to-root Wolverton components?

Ideally, a Do-It-Yourself system would utilize three air-exposure methods: (1) activated charcoal with soil or porous rock, (2) dedicated root-to-air space, (3) a fan.

First air-exposure component: Activated charcoal

In all of the plant experiments, activated charcoal has played a role.

According to a Wikipedia article:

Activated carbon, also called activated charcoal, activated coal, or carbo activatus, is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions.[1] Activated is sometimes substituted with active.

Due to its high degree of microporosity, just one gram of activated carbon has a surface area in excess of 500 m2, as determined by gas adsorption [i.e., adhesion to a surface]. An activation level sufficient for useful application may be attained solely from high surface area; however, further chemical treatment often enhances adsorption properties.

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Activated carbon is used in gas purification, decaffeination, gold purification, metal extraction, water purification, medicine, sewage treatment, air filters in gas masks and respirators, filters in compressed air and many other applications.

The Wikipedia article describes different types of activated charcoal, and different uses to which those types may be put to purify air, water, metal, or other substances. Insight into how activated charcoal may accomplish so many functions is seen in Dewar’s description of how temperature affects adsorption capability and storage of a substance within activated charcoal:

James Dewar, the scientist after whom the Dewar (vacuum flask) is named, spent much time studying activated carbon and published a paper regarding its adsorption capacity with regard to gases.[13] In this paper, he discovered that cooling the carbon to liquid nitrogen temperatures allowed it to adsorb significant quantities of numerous air gases, among others, that could then be recollected by simply allowing the carbon to warm again and that coconut based carbon was superior for the effect. He uses oxygen as an example, wherein the activated carbon would typically adsorb the atmospheric concentration (21%) under standard conditions, but release over 80% oxygen if the carbon was first cooled to low temperatures.

The Wikipedia article provides a footnote #14 referencing a list of common industrial and agricultural gases adsorbed by activated carbon can be found online.

Source: Wikipedia: Activated Carbon.

Wolverton described the action of the activated carbon thusly:

The activated carbon absorbs large quantities of the toxic chemicals and retains them until the plant roots and associated microorganisms degrade and assimilate these chemicals.

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As air is drawn through the hydroculture (sterilized stone) potting media and activated carbon granules, toxins are attracted to the carbon surfaces where root-associated microbes then feed on them, changing the toxins into harmless substances that are used as food by the plant in the pot.

Source: Wolverton Techbrief.

Click next page to see the second root-to-air Do-It-Yourself plant air filter component.