NICT and Asahi Kasei Corporation develop UV LED module for air sterilization inside trains

A research group led by Director Shin-ichiro Inoue of the DUV ICT Device Advanced Development Center, Advanced ICT Research Institute at the National Institute of Information and Communications Technology (NICT), in collaboration with Asahi Kasei Corporation, has developed an air sterilization module for railway vehicles equipped with a high-intensity deep ultraviolet LED with an emission wavelength of 265 nanometers. The research group installed the module on an in-service train of Shizuoka Railway and demonstrated the performance of the module.

The group is advancing studies on aluminum gallium nitride (AlGaN)-based deep ultraviolet LEDs using nano-optical structure technology and is developing a watt-class deep UV LED handheld irradiation device comparable to mercury lamps. NICT has succeeded in developing the world's first deep UV LED capable of controlling the light distribution angle, enabling efficient irradiation of only the necessary areas with deep UV light without using lenses or optical components. Furthermore, in collaboration with the Institute of Medical Science at the University of Tokyo, they have become the first in the world to quantitatively demonstrate that deep UV LEDs with an emission wavelength of 265 nanometers are extremely effective at inactivating airborne COVID-19.

In the wake of the COVID-19 pandemic, the importance of hygiene management in public transportation has become even more significant. In environments like railway cars, where large numbers of people spend extended periods of time in enclosed spaces, reducing the risk of aerosol transmission has become an urgent issue. However, traditional deep ultraviolet sterilization has had challenges, such as the use of lamps that contain mercury, which is harmful to humans and the environment, and are prone to breaking. Additionally, issues arose with the size of the light source and the need for large power supplies. While deep UV LEDs have excellent characteristics such as being compact, having low environmental impact, and offering long lifespans, their output has been weak.

To address these issues, NICT and Asahi Kasei collaborated as the former possesses high-intensity deep ultraviolet LED technology with a performance level comparable with that of mercury lamps and the latter has a proven track record of mass manufacturing and application development relating to deep ultraviolet LEDs. They successfully developed a high-intensity deep UV LED air sterilization module for trains with low environmental loads and power consumption. This compact module was installed into the ceiling of a railway vehicle on the Shizuoka Railway to examine its performance. It draws in air containing viruses from inside the vehicle, and after inactivating them with deep ultraviolet light, discharges clean air back into the environment.

To evaluate the inactivation performance against airborne viruses, a test virus (Escherichia coli phage MS2) was sprayed into a 25-cubic meter space using an aerosol generator. The amount of virus inactivation relative to the module's power consumption and operating time was measured using the plaque method. For comparison, a reference module using a low-pressure mercury lamp was fabricated, and the same experiment was conducted. A comparison in terms of the power consumption required for 99.9% virus inactivation confirmed that the high-intensity deep ultraviolet LED air sterilization module was 40.7% lower than the mercury lamp module. The operation of the module installed on the in-service passenger train was tested for one month, and the safe and stable operation was confirmed.

Another module of the same type with multiple deep UV LEDs with 500-milliwatt output was tested. The test confirmed that 90% of the viruses were inactivated after 35 minutes of operation of the deep ultraviolet LED modules, 99% after 71 minutes, and 99.9% after 106 minutes. The mercury lamp module took 188 minutes to inactivate 99.9%. It has been demonstrated that the time required for inactivation by the module developed by the research group is 43.6% shorter than that required by the mercury lamp module.

Moving forward, NICT and Asahi Kasei will, in collaboration with related corporations, put forth efforts for social implementation of the high-intensity deep ultraviolet LED air sterilization module.