A system for reducing airborne contamination includes a housing defining the structure of the system and configured to fit within a window of a building. The system also includes a variable-speed fan, and a microprocessor in communication with the fan and configured to control the speed of the fan. Within the housing, the system may include an electrical chassis that defines a chamber and supports at least some of the system's electrical components within the housing. A removable cartridge may be selectively coupled with the electrical chassis to form a germicidal radiation chamber within the housing and within an airflow path through the system. The removable cartridge includes UV light source(s) and filter(s) that sterilize the air as it passes through the system and the germicidal radiation chamber.
