Size-resolved fluorescent biological aerosol particle concentrations and occupant emissions in a university classroom

This study is among the first to apply laser-induced fluorescence to characterize bioaerosols at high time and size resolution in an occupied, common-use indoor environment. Using an ultraviolet aerodynamic particle sizer, we characterized total and fluorescent biological aerosol particle (FBAP) levels (1-15m diameter) in a classroom, sampling with 5-min resolution continuously during eighteen occupied and eight unoccupied days distributed throughout a one-year period. A material-balance model was applied to quantify per-person FBAP emission rates as a function of particle size. Day-to-day and seasonal changes in FBAP number concentration (N-F) values in the classroom were small compared to the variability within a day that was attributable to variable levels of occupancy, occupant activities, and the operational state of the ventilation system. Occupancy conditions characteristic of lecture classes were associated with mean N-F source strengths of 2x10(6) particles/h/person, and 9x10(4) particles per metabolic g CO2. During transitions between lectures, occupant activity was more vigorous, and estimated mean, per-person N-F emissions were 0.8x10(6) particles per transition. The observed classroom peak in FBAP size at 3-4m is similar to the peak in fluorescent and biological aerosols reported from several studies outdoors.