Acid gas

Acid gas is a particular typology of natural gas or any other gas mixture containing significant quantities of hydrogen sulfide (H₂S), carbon dioxide (CO₂), or similar acidic gases. A gas is determined to be acidic or not after it is mixed with water. The pH scale ranges from 0 to 14, anything above 7 is basic while anything below 7 is acidic. Water has a neutral pH of 7 so once a gas is mixed with water, if the resulting mixture has a pH of less than 7 that means it is an acidic gas; if the pH is more than 7, that means it is an alkaline gas.^[1]

The term/s acid gas and sour gas are often incorrectly treated as synonyms. Strictly speaking, a sour gas is any gas that specifically contains hydrogen sulfide in significant amounts; an acid gas is any gas that contains significant amounts of acidic gases such as carbon dioxide (CO₂) or hydrogen sulfide. Thus, carbon dioxide by itself is an acid gas but not a sour gas.