Air purification and microbiological sanitization system for a heating, ventilation, or air conditioning system of a railway vehicle, or the like, the purification and microbiological sanitization system comprising: a casing, adapted to define therein a purification and microbiological sanitization chamber, and having an inlet opening adapted to allow the inflow of air into the purification and microbiological sanitization chamber and an outlet opening adapted to allow the outflow of air from the purification and microbiological sanitization chamber; an ionizer device adapted to ionize at least partially the air contained within said purification and microbiological sanitization chamber of the casing; an electronic control unit configured to control the purification and microbiological sanitization system; and an air quality sensor adapted to measure a particulate matter concentration and a carbon dioxide concentration in the air at said outlet opening, to generate a respective measurement signal (Sp) representative of said measurements, and to transmit it to said electronic control unit, characterized in that it further comprises a plurality of light-emitting diodes each adapted to generate a germicidal ultraviolet radiation having a wavelength between 100 nanometers and 300 nanometers and to emit said radiation inside said purification and microbiological sanitization chamber of the casing; wherein the electronic control unit is configured to control the radiant power of at least one light-emitting diode as a function of the measurement signal (Sp) transmitted by the air quality sensor, wherein said purification and microbiological sanitation chamber is divided into a plurality of ducts arranged side by side, and wherein at least one respective light-emitting diode of said plurality of light-emitting diodes is arranged inside each of said ducts. a casing, adapted to define therein a purification and microbiological sanitization chamber, and having an inlet opening adapted to allow the inflow of air into the purification and microbiological sanitization chamber and an outlet opening adapted to allow the outflow of air from the purification and microbiological sanitization chamber; an ionizer device adapted to ionize at least partially the air contained within said purification and microbiological sanitization chamber of the casing; an electronic control unit configured to control the purification and microbiological sanitization system; and an air quality sensor adapted to measure a particulate matter concentration and a carbon dioxide concentration in the air at said outlet opening, to generate a respective measurement signal (Sp) representative of said measurements, and to transmit it to said electronic control unit, characterized in that it further comprises a plurality of light-emitting diodes each adapted to generate a germicidal ultraviolet radiation having a wavelength between 100 nanometers and 300 nanometers and to emit said radiation inside said purification and microbiological sanitization chamber of the casing; wherein the electronic control unit is configured to control the radiant power of at least one light-emitting diode as a function of the measurement signal (Sp) transmitted by the air quality sensor, wherein said purification and microbiological sanitation chamber is divided into a plurality of ducts arranged side by side, and wherein at least one respective light-emitting diode of said plurality of light-emitting diodes is arranged inside each of said ducts.