Investigating the impact of physical barriers on air change effectiveness and aerosol transmission under mixing air distribution

Abstract

This research investigated the effectiveness of desk partitions in reducing airborne infection risks in classroom environments. Experiments were conducted in a controlled test chamber with two designs of mixing air distribution systems (MV1 and MV2). Nebulized aerosols and bioaerosols were utilized in the presence of physical barriers to simulate the transmission of exhaled droplets from a source of infection and to assess this transmission among individuals sitting near this source. In addition, local air change effectiveness (ACE) was evaluated based on age of air measurements using CO₂ tracer gas decay method. Results showed that air change effectiveness without partitions were higher than with partitions for both systems, indicating that partitions create an obstacle for effective ventilation air distribution. Moreover, MV1 exhibited significant ACE reductions at some points with partitions, while MV2 maintained high ACE values across all points. For aerosol measurements, MV2 achieved high concentration reduction rates (C_R) around 0.8 across all points, whereas MV1 exhibited mixed results, with some points showing negative C_R values due to airflow obstruction. For bioaerosol generation bacteria Micrococcus luteus was used. Sampling of bioaerosol measured Micrococcus luteus concentrations, 4- and 45-minutes post-generation. MV2 system was more effective in reducing bacterial concentrations with partitions, while MV1 showed variable results, with partitions reducing concentrations at some points but increasing them at others. Overall, MV2 demonstrated superior performance in maintaining lower contaminant concentrations, especially for environments requiring prevention measures or where maintaining well-mixed air is difficult.