Particulate matter in mechanically ventilated high school classrooms

This two year study is based on measurements of particulate matter (PM) in seven high schools in Central Texas, each with mechanical ventilation. Measurements were completed in 39 classrooms, including five portable (temporary) classrooms. Each classroom was sampled between one and four four-day sampling events. The average PM2.5 and PM10 concentrations in the classrooms were lower than standards established by WHO and ASHRAE. The I/O ratios for PM2.5 and PM10 in this study were much lower than those reported in many other related studies, which may be due to use of filtration systems in all schools that participated in this study. Indoor PM1 and PM2.5 concentrations correlated with outdoor concentrations. However, indoor and outdoor PM10 did not correlate, indicating that the primary source of indoor PM10 is resuspension from indoor surfaces, specifically flooring. There was no significant difference in size-resolved particulate matter between regular (permanent)and portable classrooms during school hours. Flooring type had a significant effect on indoor PM. For PM1, PM2.5 and PM10, carpet flooring was associated with 1.4, 1.8, and 3.8 times higher indoor concentrations relative to classrooms containing vinyl composition tile (VCT) flooring. The average PM emission rates per student in regular classrooms with VCT, regular classrooms with carpet, and portable classrooms with carpet were 0.10 mg/ h, 0.11 mg/h and 0.12 mg/h for PM2.5 and 0.51 mg/h, 1.84 mg/h and 1.59 mg/h for PM10. The reported PM emission rates described herein can be used to better estimate indoor PM concentrations in classrooms.