Chemistry Reference
In-Depth Information
Table 1 Infiltration factors
estimated as regression slope
for the relationships between
indoor and outdoor 24-h
average concentrations of
different particle metrics from
RUPIOH study [
13
]
Helsinki Athens Amsterdam Birmingham
PM
2.5
0.48
0.42
0.39
0.34
PM
10
-PM
2.5
0.14
0.16
0.11
0.13
PNC
0.42
0.42
0.19
0.22
Soot
0.63
0.84
0.78
0.71
Sulfate
0.59
0.61
0.78
0.61
Several studies in the USA that measured particle size distributions have also found
lower infiltration factors for particles in the ultrafine range [
17
,
18
,
20
,
21
]. In a
study in nine Boston homes without smokers, the infiltration factor for particles
between 0.02 and 0.1
m was between 0.5 and 0.7, whereas it was 0.28 for coarse
particles and 0.74 for PM
2.5
[
16
]. In a study of 17 Los Angeles homes, the
infiltration factor was 0.75 for particles between 0.08 and 0.3
m
m
m; 0.50 for particles
m
m
between 0.02 and 0.03
m[
18
]. A study
conducted in a Helsinki office found that indoor PNC tracked outdoor
concentrations well but were only at 10% of the outdoor concentrations [
22
]. A
study in two empty hospital rooms in Erfurt, Germany reported a high correlation
and an I/O ratio of 0.42 for total PNC, compared to 0.79 for PM
2.5
[
23
]. There is
thus a large range in reported infiltration factors, related to differences in air
exchange rates, building characteristics and likely also differences in measurement
methods across studies.
A significant fraction of UFP may be volatile, particularly in particles smaller
than 50 nm [
24
,
25
]. Volatility increased with decreasing distance to a major
freeway [
24
]. In a study in four apartments near a US freeway, I/O ratios were
highest for particles of about 100 nm, decreased up to about 20 nm and then
increased again for particles smaller than 20 nm [
25
]. The pattern below 20 nm
did not agree with previous theory (Sect.
3
). A potential explanation is that upon
infiltration losses may occur of volatile components, resulting in a shift of the
particle size distribution towards particles less than 20 nm [
25
].
m and 0.17 for particles between 5 and 10
4.5
Indoor-Outdoor Relationships of Specific Particle
Components
PM
2.5
is a complex mixture of components derived from multiple sources. Major
components of PM
2.5
include secondary inorganic components (sulfate, nitrate),
elemental carbon and organic carbon. Infiltration factors and indoor sources differ
for these components, as illustrated in Table
1
.
