Summary form only given. In atmospheric-pressure gas discharge system, slit discharge (SD), has been developed for the removing of biological and chemical contaminants from the ambient air. The system consists of multiple plasma grids stacked perpendicularly to the air flow. The performance of the system has been tested using the surrogates of biological and chemical warfare agents. The results of the biological testing will be presented. The experiments have been done using the "in-room" and "in-duct" scenarios, simulating the stand alone room air cleaner and the HVAC system. The efficacy of the system in removal of bacterial spores will be presented as a function of flow rate, discharge power, number of plasma grids, and concentration of the spores in the air. Sampling methods and associated challenges will be discussed. Slit discharge (SD) is a promising technology in air-cleaning. Its performance is comparable with and often exceeds that of the convectional methods, such as dilution ventilation, filtration and ultraviolet germicidal irradiation. SD is an energy efficient, high performance, and low cost technology for air decontamination with potential uses in industry, health care and household applications