A dispersal unit for use in treating perishable goods in a storage volume to control microbial growth, the dispersal unit comprising: a housing an airflow passage in the housing an impeller for driving a flow of air through the airflow passage a support for supporting at least one replaceable cartridge in communication with the airflow passage and a vapouriser for promoting vapourisation of a volatile antimicrobial active material in a cartridge supported by the support to release an antimicrobial vapour from the cartridge into the airflow passage to be entrained in the flow of air and expelled from the airflow passage into the storage volume. The support is a base wall of a shallow vapourisation chamber that incorporates the airflow passage between the base wall and an upper wall spaced from the base wall and has openings between the base wall and the upper wall defining an inlet and an out let of the vapourisation chamber The height of the vapourisation chamber between the base wall and the upper wall is less than 40% of a width or length of the base wall.
