dioxide
Chemistry term used as a noun or prefix to indicate a compound with two oxygen atoms, e.g., 二酸化炭素 (carbon dioxide).
Carbon dioxide is one of the greenhouse gases.
Sulfur dioxide is contained in volcanic gases.
Compound of 二 (two) + 酸化 (oxidation), literally 'two-oxidation', a straightforward chemical naming pattern.
carbon dioxide fixation
carbon emission right; right to emit carbon dioxide