Abstract: An air purification and microbiological sanitization system for a heating, ventilation, and air conditioning (HVAC) system of railway vehicle includes a casing with a chamber having an inlet opening for inflow of air into the chamber and an outlet opening for outflow of air from the chamber, a plurality of light-emitting diodes (LEDs) for generating germicidal ultraviolet radiation in the chamber, an ionizer device for ionizing air in the chamber, an electronic control unit for controlling the HVAC system, and an air quality sensor for measuring concentration of particulate matter and of carbon dioxide in the air. The electronic control unit controls the radiant power of at least one LED as a function of a measurement signal transmitted by the air quality sensor.