A gas conversion apparatus (100) for converting a process gas to one or more other gases comprises: means (105) for introducing process gas into a liquid medium in a column (125); and an ultrasonic energy generator (140) arranged to generate ultrasonic energy, the apparatus (100) being configured to launch ultrasonic energy generated by the generator (140) into the liquid medium such that process gas is exposed to ultrasonic energy, the apparatus (100) being arranged to allow collection of process gas that has been exposed to ultrasonic energy. The apparatus (100) also preferably comprises a microbubble generator (120) to generate microbubbles of the process gas for exposure to the ultrasonic energy. The ultrasonic energy generator (140) may be configured to generate ultrasonic energy as a consequence of a flow of a drive gas therethrough.