Effectiveness of Particle Air Purifiers in Improving the Air Quality in Classrooms in Three Urban Public Schools in the Northeastern United States

Abstract

This study investigates whether Particle Air Purifiers (PAPs) are effective in improving indoor air quality (IAQ) in an urban school setting by removing PM2.5 and its elemental constituents from classroom air. In addition, the study examines whether seasonal differences in removal efficiency (RE) exist. Background: PM2.5 found in indoor environments has both indoor and outdoor sources. The fraction of outdoor PM2.5 found indoors is related to local outdoor air pollution levels and the condition, age and construction features of a building that increase air exchange. Urban schools that are near major roadways would be expected to have a higher fraction of PM2.5 in classroom air originating from outdoor sources. The American child spends most of his or her time indoors therefore, IAQ is very important since exposure to PM2.5 is associated with asthma and other respiratory illnesses. As well as home IAQ, Classroom IAQ is important since a child spends a significant portion of time in the school environment. Methods: Three schools (A, B, and C) in an urban school district in the northeastern United States participated in this study. There were 21 study classrooms. 11 classrooms had an active PAP with a filter and 10 classrooms had a sham PAP with no filter. Background measurements of air were taken in all classrooms prior to sham or filter cleaner placement. Two measuring periods followed background measurement. These measuring periods were Trial 1 (during winter months) followed by Trial 2 (during spring/summer months). During each trial, PAP removal efficiency (RE) was estimated for each school by comparing concentration means for sham vs. filter classrooms. F- and t-tests were performed to determine if RE results for PM2.5 and its constituents were statistically significant. A linear regression model was used to examine whether an association might exist between “leakiness” (air exchange) of classrooms and the RE of particles of outdoor origin. Results: PM2.5 concentrations were lowered in classrooms with active filters in all schools and in both trials. Mean total mass RE was 45.8% was in Trial 1 and 53.8% in Trial 2. Seasonal differences in total mass removal were significant only in School C and trivial for Schools A and B. A correlation coefficient of 0.6 showed moderate association between building leakiness and PM2.5 of outdoor origin. F- and t-test results were significant for PM2.5 in all schools and both trials, for S in all schools and both trials except for School B in Trial 1, for Si in School A in Trial 1 and School B in Trial 2; for Cl in School B in Trial 2, for K in both Trials in Schools A and C, and not Signficant for Ca and Fe in any school or either trial. Conclusions: PAPs were effective in lowering concentrations of PM2.5 and have variable effectiveness in removing its elemental constituents. More reliable results would likely be found in school buildings that are more uniform in design with classrooms that have more similar conditions than those of this study. Since PM2.5 is associated with respiratory illness in children, PAPs may be a useful tool for lowering exposure to indoor air pollutants.