Real-time Monitoring of Bioaerosol in a Residential Property in Central Tokyo

Real-time onsite monitoring of indoor airborne microbes in a residential property in central Tokyo was carried out in 2020 and 2021, following the onset of the COVID-19 pandemic. A microbial sensor utilizing fluorescence emitted by microorganisms was used to measure bioaerosol concentrations in the living room and children’s bedroom as well as on the balcony. Indoor PM_2.5 was also monitored simultaneously at certain time points using a PM_2.5 sensor. The behavior of the residents was also recorded during some monitoring periods. The average number concentration of microbes as fungi in the living room was 15,100, 58,800, and 10,600 counts m⁻³ in spring, summer, and winter, respectively, increasing in summer when the outside temperature was high. Microbial number concentrations were closely related to human behavior, increasing rapidly during periods of physical activity, but decreasing again within 20–30 min of the activity ending. There was no clear correlation between indoor microbial number concentrations and PM_2.5 concentrations, suggesting that indoor microorganisms are concentrated in coarse particles, such as dust, which are quickly removed via gravitational settling. The concentration of indoor airborne microorganisms decreased significantly after ventilation, and although an occasional increase was observed immediately after ventilation, concentrations decreased again rapidly within 10–20 min. These results suggest that even a short period of ventilation can significantly reduce the indoor bioaerosol.