an air - handling unit includes a primary air plenum and a primary air inlet in fluid communication with the primary air plenum . the primary air inlet is configured to provide a flow of primary air to the primary air plenum . the air - handling unit also includes a chamber in fluid communication with the primary air plenum . the chamber includes an irradiate cavity and a secondary air inlet configured to accept a flow of secondary air into the irradiate cavity , and a sterilization mechanism positioned in the irradiate cavity . the sterilization mechanism is configured to effectively treat and sterilize the secondary air .