The purpose of this investigation is
to know the long-term characteristics of VOC concentrations in houses built before the building code
in 2003 and to clarify the countermeasures against indoor air pollution in the
houses already built. For example, the improvements of living habits,
ventilation and the remove of building materials. The concentrations of VOCs
were measured in these houses in summer and winter from 2000 to 2005. The
results showed that the concentration of formaldehyde decreased in the first
year. After that the decline of the concentration was not seen and the concentration
changed only with the temperature. The characteristics of decline were thought
to be caused by two sorts of emission. One is an emission of concealed
formaldehyde in the process of material production and the other is an emission
with the generation of formaldehyde from adhesives of urea resin and moisture.
The concentration of toluene decreased rapidly in the first year. The
concentrations of xylene, ethyl-benzene and styrene showed a similar change.
But the concentrations of acetaldehyde which were measured from the summer of
2002 did not decrease and its concentration in some houses was higher than the
guideline even in the winter of 2005.