Mitigation of airborne contaminants in classrooms and meeting rooms with ventilation, air cleaning, and structural measures
Year: 2026
Type: dissertation
Abstract: Airborne contaminant transmission in indoor environments poses challenges to occupant health, safety, and comfort, particularly in densely occupied spaces. This dissertation investigates ventilation- and air-cleaning-based strategies to reduce airborne contaminant exposure, with a focus on source-capture systems, air distribution methods, air-cleaning devices, and structural measures. Meeting rooms and classrooms are examined as representative environments due to their high occupancy density and short interpersonal distances. The research combines laboratory experiments, field measurements, and numerical simulations to evaluate airborne contaminant mitigation under steady-state conditions. A meeting-room setting was implemented in a laboratory environment, while classroom measurements were conducted in a real classroom. Tracer gas experiments in both environments were used to evaluate ventilation efficiency and contaminant removal associated with breathing emissions. Moreover, aerosol particle measurements were conducted in the meeting room to assess the effectiveness of air-cleaning strategies during breathing and coughing. Classroom field measurements were used to validate steady-state CFD simulations of airflow and contaminant transport under different air distribution and exhaust configurations. The results indicate that ventilation effectiveness depends significantly on the supply air distribution strategy, exhaust placement, infector location, and heat-gain levels. Meeting room aerosol measurements further show that mitigation effectiveness varies with the type of respiratory emission. Face masks are the only strategy that remains effective for both breathing and coughing, providing approximately a 60% reduction in exposure when properly worn. Portable air purifiers with a clean air delivery rate (CADR) of 86 l/s, approximately 2.5 times the ventilation rate, reduce contaminant concentrations for exposed occupants, achieving around a 45% reduction during breathing. Their effectiveness is lower for coughing-related emissions. Physical barriers, on the other hand, offer protection mainly against coughing particles but are ineffective against breathingrelated aerosols. On the other hand, local exhaust systems combined with stratification-based air distribution performed best among ventilation measures. In meeting rooms, local exhausts above each workstation with a lowered ceiling improved local air quality by about 35% compared to scenarios without local exhausts. In classrooms, local exhausts were installed above the occupied zone with a lowered ceiling. The system was evaluated at three different infector positions and achieved a 45% reduction in average breathing-zone concentrations compared with mixing ventilation. It also reduced the number of occupants in the high-infection-risk category, according to the study’s risk scale, to a maximum of two, the lowest across all classroom scenarios. Multipoint ceiling-mounted exhausts were also examined, but their performance varied with the infector location. In contrast, the local exhaust system was effective for all tested infector positions, making it a reliable and practical mitigation strategy. This dissertation advances the understanding of airborne contaminant mitigation in indoor environments and provides guidance for ventilation, local exhaust, air-cleaning, and other mitigation strategies for healthier meeting rooms and classrooms.
Source: Aaltodoc (Aalto University)
Author: Ejaz, Muhammad Farhan
Language: English
Subfield: Pulmonary and Respiratory Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7204372325