Comprising of a chamber mounted dispersion tube, through which SO2 gas can be introduced, at a rate determined by the user adjustable control valve, and monitored by a flowmeter. The gas can be switched on and off automatically, at user programmable times. Designed to enable chambers to meet the requirements of ASTM G85 annex 4, and similar tests. Note: the provision of the SO2 gas cylinder and connector are the user’s responsibility and is not included as part of this option.