Analysis of time- and size-resolved fluorescent biological aerosol particles in a subway station

Subway stations are dynamic underground environments where air quality changes rapidly, primarily due to passenger occupancy patterns and the frequent arrival and departure of trains. However, traditional microbial monitoring methods are constrained by their temporal resolutions. To address this, we employed a real-time light-induced fluorescence-based bioaerosol monitoring instrument to detect the dynamics of particulate matters (PM) and classify them into fluorescent biological aerosol particles (FBAPs) or non-FBAPs based on the intrinsic fluorescent feature of bioaerosols. We deployed this sensor on the platform, in the station hall, and outdoors at a typical subway station for 18 days in Tianjin, China. The results showed that FBAP and non-FBAP concentrations on the platform were roughly 2 and 3 times higher, respectively, than those in the station hall, and approximately 3 and 4 times higher than outdoor levels. Notably, the bacteria-like particle levels on the platform were 20 times higher than those outdoor values during most periods. The concentrations of PM, dominated by non-FBAP, peaked during the morning rush hours both on the platform and in the station hall, while the bacteria-like particles reached their lowest levels in the morning, presumably caused by the elevated metal particle levels when trains started operating that inhibit bacterial survival. Train operations strongly influenced non-FBAP concentrations on the platform, as evidenced by the 7-min periodic cycle in the particle autocorrelations corresponding to train schedules. By contrast, the particle levels in the station hall did not show train-related patterns in autocorrelations but showed stronger correlations with the environmental parameters. The revealed dynamic patterns of non-biological and biological airborne particles in the subway station provide insights for mitigating particle exposure in the future.