Contributions of ambient air, indoor activity, and an air purifier to classroom PM2.5 levels in three elementary schools

Abstract

Exposure to indoor air pollutants significantly impacts human health, particularly among students who are more susceptible to particulate matter than adults and spend substantial time in schools. This study explores the influence of ambient PM_2.5 on in-classroom concentrations and assesses the extent to which in-class activities contribute to indoor PM_2.5 levels, which is crucial for effective school air quality management. PM_2.5 concentrations were monitored simultaneously inside classrooms and outdoors across elementary schools situated in three different environments. Outdoor CO concentrations, as a surrogate of fuel combustion sources around the schools, were also measured along with PM_2.5 to examine the local emission sources. Additionally, the effects of atmospheric turbulence intensity on outdoor and in-classroom PM_2.5 levels were investigated. In-classroom PM_2.5 concentrations mirrored outdoor concentration variations but with time delays of 100 – 121 min during unoccupied periods. Mean CO and PM_2.5 concentrations near the port, a significant emission source, were higher than those around the school, suggesting local air quality is influenced by wind patterns, as shown by a pollution rose analysis. Using multivariate regression based on a mass balance equation, we estimated the contributions of outdoor PM_2.5 levels to in-class concentrations to be 77%. Additionally, ambient turbulence intensity strongly correlated with both indoor and outdoor PM_2.5 concentrations, with outdoor concentrations decreasing more conspicuously in response to stronger turbulence intensity than indoor levels, thereby raising the indoor/outdoor (I/O) ratios. These findings provide insights into managing in-classroom PM_2.5 concentrations in schools by considering external pollution dynamics.