Title

Effects of location, classroom orientation, and air change rate on potential aerosol exposure: an experimental and computational study

Contributing USMA Research Unit(s)

Civil and Mechanical Engineering, Geography and Environmental Engineering

Publication Date

Spring 3-4-2022

Publication Title

Environmental Science: Processes and Impacts

Document Type

Article

Abstract

This study examined the dispersion of potentially infectious aerosols in classrooms by means of both a CO2 tracer gas, and multizone contaminant transport modeling. A total of 20 tests were conducted in three different university classrooms at multiple air change rates (4.4-9.7/hr), each with two different room orientations: one with the tracer gas released from six student desks toward the air return, and one with the same tracer gas released away from it. Resulting tracer concentrations were measured by 19 different monitors arrayed throughout the room. Steady-state, mean tracer gas concentrations were calculated in six instructor zones (A-F) around the periphery of the room, with the results normalized by the concentration at the return, which was assumed to be representative of the well-mixed volume of the room. Across all classrooms, zones farthest from the return (C,D) had the lowest mean normalized concentrations (0.75), while those closest to the return (A,F) had the highest (0.95). This effect was consistent across room orientations (release both toward and away from the return), and air change rates. In addition, all zones around the periphery of the room had a significantly lower concentration than those adjacent to the sources. Increasing the ventilation rate reduced tracer gas concentrations significantly. Similar trends were observed via a novel approach to CONTAM modeling of the same rooms. These results indicate that informed selection of teaching location within the classroom could reduce instructor exposure.

Environmental significance

Maintaining healthy air in classrooms is critical to preventing the spread of airborne viruses, and instructors are often in higher risk categories than students. This study indicates that higher ventilation rates coupled with careful selection of teaching location (on the periphery of the room, farthest from the return if possible) could potentially decrease instructor exposure to infectious aerosols.

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