Indoor/Outdoor relationships of airborne particles under controlled pressure difference across the building envelope in Korean multifamily apartments

This study investigates indoor/outdoor relationships of airborne particles under controlled pressure difference across the building envelope in Korean multifamily apartments. On-site field experiments on 14 apartment housing units located in urban areas in Korea are conducted to measure the indoor/outdoor ratios of number concentrations of size-resolved particles (0.3-0.5, 0.5-1.0, 1.0-3.0, 3.0-5.0, 5.0-10.0, > 10.0 μm). To set identical pressure difference conditions across the envelope of each housing unit for better comparison of I/O ratio results, and to examine the effect of pressure difference on the I/O relations, indoor-outdoor pressure difference was controlled at 10, 30, and 50 Pa using a blower door depressurization procedure. Simultaneously, the air leakage characteristics of housing units are measured using the typical blower door pressurization-depressurization test method to correlate air leakage data and I/O ratios. As expected, moderately airtight housing units (ACH₅₀ ≤ 4.4) show lower I/O ratios than average leaky housing units (ACH₅₀ > 4.4); still, the averaged I/O ratios of finer sized particles (0.3-0.5, 0.5-1.0, and 1.0-3.0 μm) in the moderately airtight housing units were 0.75, 0.59, and 0.61 at an I-O pressure difference of 50 Pa, and 0.62, 0.51, and 0.49 at 10 Pa. The study indicates that indoor residents in moderately airtight Korean multifamily housing units with relatively small envelope area can still be exposed to high concentrations of outdoor originated fine particles.