Chemistry Reference
In-Depth Information
Fig. 7 Infiltration factors for
PM
2.5
and soot (EC, BC)
measured in the same study.
Numbers for Hoek
2008
are
averages for four cities
1
0,8
0,6
0,4
0,2
0
PM2.5
Soot
4.5.3 Organic Carbon
There is much more limited information available on infiltration of organic carbon
(OC), but as many components are volatile significant changes occur upon infiltra-
tion indoors. The OC measurement reflects a complex mixture of components,
including polycyclic aromatic hydrocarbons (PAH), which differ widely in volatil-
ity. In ambient air a distinction is made in primary and secondary organic
components. Organic PM components can also be formed indoors, e.g. by reactions
of organic gases with ozone. Measurement of particulate OC is complicated as gas
phase artifacts may occur, resulting both in positive and negative biases [
33
]. In a
study in an unoccupied home in California, significant losses of OC were found due
to volatilization upon infiltration in the home [
33
]. In the RIOPA study, the
indoor-outdoor regression slope was 0.4 for OC, about half the slope for EC [
15
].
The contribution of outdoor OC to indoor OC was estimated at 22% only. High
indoor OC in PM
10
concentrations in schools in Aveiro, Portugal was found which
were explained for 26% by ambient OC and further by small paper, skin, and cloth
particles [
34
]. A study in Cracow, Poland showed that personal exposure of
pregnant women to PAH was explained for typically 90% by the outdoor concen-
tration [
35
].
5 Conclusions
Outdoor air pollution significantly infiltrates in buildings. Combined with the large
fraction of time that people typically spend indoors, a major fraction of human
exposure to outdoor pollutants occurs indoors. Understanding the factors affecting
infiltration is therefore important. Infiltration factors have been shown to vary
substantially across seasons, individual homes, and particle size and components.
Important factors contributing to these variations include air exchange rate,
characteristics of the building envelop (e.g., geometry of cracks), type of ventila-
tion, and use of filtration. Penetration and decay losses are particle size dependent
