Environmental Engineering Reference
In-Depth Information
(HCHO levels would decline more rapidly) with increasing temperature,
relative humidity, and ventilation. Interaction effects described below would,
if all other factors were standardized, likely increase the time period required
for a 50% reduction in HCHO levels.
In building environments that contain multiple
UF-based emission sources, measured concentrations are typically similar
or are slightly above sources with the highest emission potential present
(most potent source) rather than the sum of emissions/emission potentials
of all formaldehyde-emitting sources. Such interaction effects are due to a
vapor pressure phenomenon. High vapor concentrations associated with
emissions from potent sources suppress emissions from less potent sources.
d.
Interaction effects.
Ventilation associated with infiltration, opening win-
dows, and mechanical induction can affect indoor concentrations of HCHO
as well as emission rates. Formaldehyde levels decrease with increasing
ventilation rates. The relationship is not linear because a doubling in the
ventilation rate is associated with only a 30 to 35% decline in HCHO levels
(due to increased emission rates). Natural ventilation associated with infil-
tration appears to have a significant effect on HCHO levels. Under controlled
conditions, HCHO levels reach their maximum values when indoor/outdoor
temperature differences are small. Lowest HCHO levels in northern climates
are observed during the cold season, especially on cold winter days (
Figure
e.
Ventilation.
Since HCHO is a by-product of combustion pro-
cesses, smokers, as can be expected, are exposed to high HCHO levels (on
the order of 40 to 250 ppmv in a single puff). Formaldehyde emissions from
significantly lower levels from environmental tobacco smoke (ETS) because
of the significant dilution effects that occur. Because of interaction effects
f.
Tobacco smoke.
Relationship between indoor formaldehyde levels and outdoor
temperatures.
Figure 4.2
