Particle Concentrations and Sizes in an Air-Conditioned Office with Normal Efficiency Air Filtration of University

The indoor and outdoor particle number concentrations of different size ranges (0.3-0.5μm, 0.5-1.0μm, 1.0-3.0μm, 3.0-5.0μm, and ≥10.0μm) were measured in an air-conditioned office without tobacco smoking and fresh air. The total mass efficiency of the normal filter installed in the air handing system was measured and calculated to below the 9%, which is much smaller than the efficiency of the filters specified by ASHRAE. Experiments further revealed that the larger particles have the higher filtration efficiency, so the ratios of the concentration of the indoor to outdoor (I/O) decreased with the particles increased. And for the ranges of particle size measured (> 0.3μm), the indoor particle number concentrations were considerably less than that in outdoor. But for the ratios of I/O, there is a sharp down before the 2.0μm and then a slightly decline.