A modular ductwork assembly decontaminates an air stream circulating within a heating, ventilation and air conditioning (HVAC) system. The assembly includes one or more of (a) an ionizing module for removing particulates from the air stream, (b) a sterilization module for neutralizing airborne pathogens present in the air stream, (c) an ozone treatment module for neutralizing pathogens or odoriferous constituents or volatile organic compounds (VOCs) present in the air stream, optionally (d) baffles for slowing and disrupting the flow rate and promoting turbulence in the air stream traveling through the modules and optionally (e) a fan module for directing a treated air stream, (f) an ozone sensor, (g) a monitoring or ozone control means, (h) a means of delivering and repurposing generated ozone. Each of the modules is arranged substantially adjacent to at least one of the other modules.