Acid gas is any gaseous compound which, when dissolved in water, will form an acidic solution. The most common types of acid gas are hydrogen sulphide (H2S), carbon dioxide (CO2) and organic sulfurs (such as mercaptan and COS), though there are many other varieties as well, including hydrogen chloride (HCI), hydrogen fluoride (HF), sulphur oxides (SO2 and SO3) and nitrogen oxides (NOx).

Although these substances are often found in natural gas in varying concentrations, they can be damaging to both the pipes which contain them and the humans who work in their vicinity. As a result, there are strict regulations about the concentrations of acid gas in off gas from industries which require the use of sophisticated environmental technology to achieve compliance.

The adsorption principle of the activated carbon filters is well established in acid gas removal.