Passengers on public buses operating in the metropolitan area are exposed to the closed indoor air for minutes to hours. The indoor air quality of buses is mostly controlled through ceiling-mounted ventilation and filtration devices. A simulation study using a commercial code was conducted for fluid flow analysis to evaluate the potential effectiveness of an air purifier that can be inserted into bus windows to supply clean air from the outside to the inside. As a result of field measurements, the average CO2 concentration inside the bus during morning and evening rush hours ranged from 2,106±309 ppm to 3,308 ± 255 ppm depending on the number of passengers on board. This exceeded the Guideline for Public Transportation. The optimal installation position of an air purifier appeared to be the front side of the bus. In fact, even a low diffusing flow velocity of 0.5m/s was effective enough to maintain a low concentration of CO2 throughout the indoor space. Based on numerical analysis predictions with 45 passengers on board, the maximum CO2 concentration in the breathing zone was 2,203 ppm with the operation of an air purifier.

A field study was conducted to reduce airborne bacteria by supplying active ions to indoor spaces used by vulnerable human groups spending substantial amounts of time in places such as schools and hospitals. In an experiment conducted during school hours (8:00-15:00), the average number of airborne bacteria in classrooms was 345.53 CFU/m3 or more without active ions. However, ion supply reduced the airborne bacteria to an average of 113.23 CFU/m3, indicating an efficiency of 61.61%. As a result of tests in 33 rooms used for surgery in small and middle sized hospitals, ion supply for 2 to 4 hours reduced the average airborne bacteria concentration from 243.88 CFU/m3 to 104.34 CFU/m3, representing a 41.53% reduction. A laboratory test to confirm the ion activity has shown that the mortality rate of E. coli used as a test bacterium increased with exposure time to ions. The initial colony number of E. coli was 251 CFU, but decreased to 4 CFU after 60 minutes of exposure to active ions. Therefore, it was confirmed that the supply of active ions can contribute to the control of airborne bacteria in the indoor environment of schools, hospitals and other public facilities.