Measurements and Modeling of Indoor Air Pollutants and Mitigation Scenarios in Older Educational Buildings

JIANING BAO, Nigel Kaye, Ehsan Mousavi, Christopher Post, Andrew Metcalf, Clemson University

     Abstract Number: 346
     Working Group: Indoor Air Purification Technologies, Best Practices, and their Health Impacts

Abstract
Airborne transmission of pathogens highlights the need for safer building environments regarding indoor air quality (IAQ), especially for high-occupancy spaces, including classrooms at schools and colleges. As compared to newer buildings with modern central ventilation systems, older buildings generally have less effective ventilation systems with respect to ventilation rate and filtration efficiency, which can increase the vulnerability of building occupants to exposure to poor IAQ. Thus, it is important to evaluate the efficacy of ventilation systems in maintaining optimal IAQ and to explore mitigation strategies aimed at reducing pollutant levels in older educational buildings.

In this study, we use a Scanning Electrical Mobility Spectrometer (SEMS) and low-cost sensors to evaluate IAQ by measuring the concentrations of size-resolved particulate matter (PM) and carbon dioxide (CO₂) in classrooms from two different college buildings with outdated ventilation systems. Measurements are taken during controlled CO₂ and particle releases when the space is unoccupied, and during general occupancy to capture activity-induced emissions. By analyzing the exponential decay of PM and CO₂ concentrations over time, we evaluate and compare the effectiveness of the ventilation and filtration systems in different classrooms with varied conditions, such as room sizes, ventilation setups, and the addition of filtered box fans. To further understand and explore how to improve IAQ in this classroom, we used the measurements to constrain parameters in a box model of the indoor space that can simulate CO₂ and size-resolved PM concentration under varied conditions. The box model reveals the infiltration rate to the space, which controls the trends in CO₂ and determines the level at which outdoor PM can affect IAQ. By simulating real-world scenarios, this study demonstrates that using a simple box model is a viable approach to finding feasible mitigation strategies to simultaneously address both PM and CO₂ pollution in an indoor space.