An ozone unit 5 for a shipping container 1 comprises as an integrated unit in a common casing an ozone generator, an ozone sensor or an input port for a signal from an ozone sensor, and a controller or a port for connection of a controller. The common casing is shaped and sized to be mounted partly at least within, or through, a pre-existing opening 3 through an insulated wall of a standard insulated shipping container 1 after removal of a pre-existing insulated cover 2 and so as to enable replacement of the insulated cover 2 within the opening 3 after installation of the ozone unit 5.
