Graduate Studies, UNL

 

Dissertations and Doctoral Documents from University of Nebraska-Lincoln, 2023–

First Advisor

Josephine Lau

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

James Bovaird, Moe Alahmad, Xiaoqi (Clare) Liu

Department

Architectural Engineering

Date of this Version

2025

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree Doctor of Philosophy (Ph.D.)

Major: Architectural Engineering

Under the supervision of Professor

Lincoln, Nebraska, December 2025

Comments

Copyright 2025, the author. Used by permission

Abstract

This large-scale randomized experimental field study investigated the effect of portable air purifiers (PAPs) on classroom’s air quality and student’s illness related absenteeism. PAPs were installed in 317 classrooms from various school districts located in Eastern Nebraska. The classrooms were randomly assigned into four conditions: three treatment conditions (T1, T2 & T3) and one control condition (device without any filter). T1 was equipped with HEPA filters, T2 added Activated Carbon (AC) layer to HEPA, and T3 further integrated Germicidal Ultraviolet (GUV) alongside HEPA and AC filters. The measured variables were carbon dioxide (CO2), fine particles (PN2.5) and coarse particles (PNcoarse), total volatile organic compounds (TVOC), ozone (O3), relative humidity (RH), and temperature (T). Continuous CO2 data were used to calculate ventilation rates (VR), and comparisons were made with design VRs as specified in ASHRAE Standard 62.1. PAPs did not significantly reduce TVOC or ozone levels in the tested classrooms, likely because those classrooms had low pollution levels. Generalized Linear Mixed-Effects Modeling (GLMM) was used to estimate the effect of treatment condition on particle counts and illness related absenteeism (IRA) in classrooms. The predicted coarse particle counts showed significant reductions during unoccupied time at, above, and below the Mean Design Ventilation Rate (MDVR). In contrast, during occupied time, there were significant reductions at and below MDVR, but a slight increase above MDVR. For fine particles, significant reductions were observed during unoccupied time across all treatments, whereas during occupied time, reductions were observed for T1 & T2 but not for T3. VR had no significant effect on fine particles but affected filter performance for coarse particles. The impact of VR with and without PAPs on students' Illness-Related Absenteeism (IRA) was modeled. 7-day, 10-day, and daily VR models were used to predict IRA across Fall, Winter and Spring seasons. The model predictions showed an increase in IRA with the increase in daily VR but a decrease with the increase in average school level VR. The increase in average classroom level VR was also associated with decrease in IRA except in fall season.

Advisor: Josephine Lau

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