Developing and testing VOC mitigating materials is an ongoing challenge. While a variety of porous materials that adsorb small molecules have been realized, in practice activated carbon is widely used for VOC removal due to its low cost, durability, ease of use, low hydrodynamic resistance, wide-spread commercial availability and general flexibility in interfacing with various equipment types. Additionally, activated carbon requires no external energy source such as heating or irradiation in order to function via physisorption, nor does it require cooling to low temperature. Activated carbon removes VOCs from the air primarily via surface adsorption, minimizing the likelihood of undesired byproducts that are associated with some materials that remove VOCs primarily via catalytic reactions. It should be noted, however, that activated carbon is a structurally rich material and its interactions with gases and liquids under various environmental parameters are not limited to physisorption. Activated carbon can be commercially obtained in various macroscopic forms including powdered, granulated and fibrous. The term activated carbon indicates that material synthesis conditions involved aggressive heating of carbonaceous material in an inert environment, which induces pyrolytic decomposition and carbonization, followed by "activation", which is a subsequent aggressive heating step in the presence of an oxidant (CO2 or steam, for example). The activation step results in preferential etching of some regions of the carbon material, which in turn increases the surface area through the creation of a polydisperse, porous, three-dimensional structure. In general, the structural features of activated carbon are complex and vary based on preparation conditions. These features include pore size and chemical composition. The expansive surface area of activated carbon creates a multitude of sites for binding small molecules. The exact properties will depend on the processing conditions and carbon source. The surface is essentially polyaromatic with varying amounts of heteroatoms. While a typical elemental composition might consist of 88% C, 0.5% H, 0.5% N, 1% S, 6-7% O and 3-4% inorganic ash, the percent weight values can deviate from these amounts with O varying from 1-20%. In at least some activated carbon materials and similar carbon-based materials persistent free radicals are present. Note that in some reports the adsorption and reactivity of activated carbon is altered via surface modification or composite formation. The complex and variable structure of activated carbon suggests that its effectiveness should be tested when introducing to air cleaning devices for specific applications.