A system comprising: a radio frequency, RF, signal source having a power output for outputting RF signals; a housing including a first cavity configured to contain a load; an RF defrost system at least partially disposed in the first cavity, the defrost system being configured to be powered by a first RF signal at a first frequency to defrost the load within the first cavity; a first air treatment device (280, 290) in fluid communication with the housing, the first air treatment device (280, 290) being configured to be powered by a second RF signal at a second frequency, and to perform a first RF air purification process in response to the second RF signal; a switching arrangement configured to selectively electrically connect the defrost system and the first air treatment device (280, 290) to the power output of the RF signal source; and a controller configured to: cause the switching arrangement to electrically connect one of the defrost system and the first air treatment device (280, 290) to the power output of the RF signal source, when the defrost system is electrically connected to the power output of the RF signal source, cause the RF signal source to output the first RF signal at the first frequency, when the first air treatment device (280, 290) is electrically connected to the power output of the RF signal source, cause the RF signal source to output the second RF signal at the second frequency, wherein the first air treatment device (280, 290) is selected from a plasma generator and a gas-discharge lamp that generates ultraviolet light by exciting plasma using RF power. a radio frequency, RF, signal source having a power output for outputting RF signals; a housing including a first cavity configured to contain a load; an RF defrost system at least partially disposed in the first cavity, the defrost system being configured to be powered by a first RF signal at a first frequency to defrost the load within the first cavity; a first air treatment device (280, 290) in fluid communication with the housing, the first air treatment device (280, 290) being configured to be powered by a second RF signal at a second frequency, and to perform a first RF air purification process in response to the second RF signal; a switching arrangement configured to selectively electrically connect the defrost system and the first air treatment device (280, 290) to the power output of the RF signal source; and a controller configured to: cause the switching arrangement to electrically connect one of the defrost system and the first air treatment device (280, 290) to the power output of the RF signal source, when the defrost system is electrically connected to the power output of the RF signal source, cause the RF signal source to output the first RF signal at the first frequency, when the first air treatment device (280, 290) is electrically connected to the power output of the RF signal source, cause the RF signal source to output the second RF signal at the second frequency, cause the switching arrangement to electrically connect one of the defrost system and the first air treatment device (280, 290) to the power output of the RF signal source, when the defrost system is electrically connected to the power output of the RF signal source, cause the RF signal source to output the first RF signal at the first frequency, when the first air treatment device (280, 290) is electrically connected to the power output of the RF signal source, cause the RF signal source to output the second RF signal at the second frequency, wherein the first air treatment device (280, 290) is selected from a plasma generator and a gas-discharge lamp that generates ultraviolet light by exciting plasma using RF power.