The formaldehyde emission experiment from porous building materials were carried out in an environmental chamber. The experimental apparatus is shown in Fig. 2. The volume of the chamber was 0.05 m3, with a metal fan in the top to promote mixing between the air and formaldehyde. The concentration of formaldehyde in the chamber emitted from the building material was monitored every 15 minutes with a formaldehyde analyzer (Interscan 4160). The formaldehyde analyzer was connected to the chamber through two teflon tubes: a gas sampling tube used for sampling the formaldehyde concentration from the chamber, and a gas return tube used for transporting the sampled gas back to the chamber to maintain the gas pressure equilibrium. The humidity (46% ~ 50%) and temperature of the laboratory was monitored and recorded throughout the experiment.