A system and method reduce a concentration of viable microorganisms, including but not limited to the 2019 novel (new) coronavirus that causes the illness coronavirus disease 2019 (COVID-19), in air in a workspace by over 80% with a single pass of air through the system. A heater heats air drawn from the workspace and a desiccant dehumidifier further heats air from the heater. The heater and desiccant dehumidifier decontaminate the air to kill or inactivate the microorganisms so that air returned to the workspace from the system has a reduced concentration of viable microorganisms.