Residences represent an important site for bioaerosol exposure because of the large proportion of time that people spend in their homes. Using real-time instrumentation, our recent study in Indoor Air investigated bioaerosol concentrations, emissions, and exposures in a northern California residence, focusing on the effect of human occupancy and activities. Using an ultraviolet aerodynamic particle sizer (UVAPS), we were able to monitor size-resolved viable biological particles in real-time (1-min time resolution) based on laser-induced fluorescence. Particle auto-fluorescence at characteristic wavelengths is considered as an indicator of active cellular metabolism. Following previous practice, we refer to the fluorescent particles measured by the UVAPS as fluorescent biological aerosol particles (FBAPs).
The house we studied is a single-family home with a floor area of 170 m2 and two adult residents. We found that human occupancy and activities are important sources of FBAPs even in this moderately large home with only two occupants. Occupancy enhanced indoor FBAP concentrations by an order of magnitude above the levels observed during unoccupied periods. In addition, common household activities, such as making a bed, can substantially emit indoor FBAPs. In central tendency, selected human activities emitted 10 to 50 million FBAP particles per event. Due to the strong influences of occupancy and activities, we suggest that only concentrations measured during occupancy periods should be used to assess FBAP exposure in residences. Including concentrations measured during unoccupied periods in exposure assessment would likely underestimate human exposure to FBAPs to a substantial extent.