Zero-Air Generator is a simple, light-weight, self-contained system capable of producing high purity, particle free, dry air at up to 18 liters per minute. It is designed to replace gas cylinders as a source of calibration standard. The ZAG can be used with stationary analyzers, but its portability makes it especially well suited for use with remote monitoring sites and mobile testing facilities. The built-in air compressor draws ambient air through a 10-micron particulate filter then drives it through a tube membrane dryer to remove moisture. The air stream exiting the dryer is split, with a portion expanded through an orifice and used as a countercurrent purge source for the dryer. The main air stream exiting the dryer continues to the ultraviolet light chamber where it is sterilized via irradiation. The ultraviolet light also serves as an oxidizer, converting NO into NO2. The air stream then flows into a carbon monoxide catalyst canister which converts CO into CO2. At this point the air enters an activated carbon canister. The activated carbon removes any hydrocarbons and acid vapors present in the air stream. In addition, an indicating catalyst blended with the carbon removes NOX. This catalyst changes from purple to brown and ultimately to white as its capacity is exhausted. Before exiting the system, the air flow trough a 0.1-micron particulate filter which ensures that there is no desiccant dust carryover from the canisters.