Measurements
Measurements of air tightness and outdoor air supply
rates were undertaken before particle sampling. Air
tightness was measured using a blower door (Minneapolis
Blower Door Model 3; TEC, St. Cloud, MN,
USA) according to ASHRAE Standard 119. All exterior
windows, diffusers, and vents for local exhaust
were closed during the air tightness measurement. The
apartments were first depressurized to 50 Pa by a fan
of the blower door, and then, the pressure was stepped
down in 10-Pa intervals. The air tightness was
expressed using a normalized leakage area and effective
leakage area at 4 Pa pressure difference.