The major indoor
source was smoking, which elevated indoor concentrations by 37 μg/m3 in the 101 homes with smokers.
Other significant sources included frying, smoky cooking events, use of incense, and apartment
housing, although the increases due to these events ranged only from 3 to 6 μg/m3. The 10-min averaging
time allowed calculation of an average diurnal variation, showing large increases in the evening due
to smoking and smaller increases at meal times due to cooking