Aerosol Chemistry and Physics - Aerosols: Measurement, Dosimetry, and Health Effects - page 155

in a liquid (Finlayson-Pitts and Pitts, 1999, p. 417), and the measured partitioning coeficient for
ab sorption takes the same form as Equation 6.2.

F
A TSP

i om ,

K = absorption into a liquid film or droplet (6.5)

p

⋅

i

F i,om represents the particle-associated concentration of i in air as measured from a ilter, with
explicit recognition that i has dissolved in liquid organic material, om, on the particle. For absorp-
tion into liquid ilms on particles, Pankow (1994) showed that K p is proportional to the weight frac-
tion of om to TSP.

f 760 RT

om
om L

K = adsorption (6.6)

p

o

10 6 MW p γ

K p is inversely proportional to the product of p o and the activity coeficient γ of i in the liquid
phase. Vapor pressure is the most important factor inluencing K p , followed by activity coeficient
and molecular weight. If the activity coeficient does not vary much across members of a class of
SVOCs, plots of K p versus log p o will have a slope of −1 for both adsorption and absorption, as in
Equations 6.4 and 6.7.

f 760 RT

o om

log K = − log p + log (6.7)

p L

6

MW γ 10

om

Recent contributions to gas/surface partitioning theory address observed deviations from the
predictions of Equations 6.4 and 6.7. Jang et al. (1997) applied a comprehensive thermodynamic
approach to calculate group contributions to activity coeficients for adsorption of SVOC into noni-
deal organic ilms. This allows calculation of activity-normalized partitioning coeficients, K p,g .
Goss and Schwarzenbach (1998) argued that slope deviations from −1 in log K p versus log p o plots
do not necessarily indicate nonequilibrium conditions, and they outlined how these deviations can
be used to identify types of sorbate/sorbent interactions and thus characterize sorption processes.
For example, they showed how acid/base interactions can inluence gas/surface partitioning polar
SVOC. Harner and Bidleman (1998) demonstrated that using laboratory-derived octanol/air parti-
tioning coeficients circumvents the need to estimate activity coeficients for compounds absorbed
in the organic ilms that coat urban particles. Mader and Pankow (2000, 2001a,b) expanded parti-
tioning theory to quartz and Telon ilter materials that are used to collect particles, thus tackling
the sticky problem of SVOC adsorption artifacts in PM sampling on ilters.

6.3.3 s urFace a rea in tHe i ndoor e nvironMent
From the perspective of indoor air quality and personal exposure, understanding the inluence of
surface area on the behavior of airborne particles includes recognizing the importance of indoor
surfaces on aerosol processing. The surface-to-volume ratio is 2 orders of magnitude greater
indoors than outdoors. Weschler's instructive discussion (Weaschler, 2003) of indoor surface
area will be recounted briely here. The example is based on a room with volume 40 m 3 and a
carpet of 10 m 2 .

6.3.3.1 Particles
In a now classic study of gas/particle partitioning, Liang et al. (1997) inferred the surface area of
their airborne particles as 2 m 2 g −1 . Using their data, Weschler (2003) calculated that surface load-
ing of a semi-volatile compound with subcooled liquid vapor pressure of 10 −6 atm (hexadecane or