Gas molecules migrate into the pores and become trapped on the surface of the carbon. The type of adsorption is categorized by the nature of the forces involved in trapping the gas molecules. Physical adsorption involves electrostatic forces similar to those that cause static cling. These forces are relatively weak and the gas molecules can be released to the air again. In contrast, chemical adsorption involves a chemical reaction between the gas and the solid, which is typically irreversible.
Adsorption is well understood for single contaminants at high concentrations.
It has been studied extensively for industrial purification and separation processes that involve fewer gases at concentrations several orders of magnitude higher than indoor concentrations. The process becomes much more complicated when many low concentration gases, including water vapor, are being adsorbed. In this case there is competition for adsorption sites, and one physically adsorbed contaminant can be replaced by another one. To further complicate matters, ozone can chemically react with other gases and with the adsorbent. Models for adsorption of chemically reactive gases, like ozone, are not available.