Aerosol Chemistry and Physics - Aerosols: Measurement, Dosimetry, and Health Effects - page 158

tracers for iniltration of outdoor PM 2.5 , but indoor PM 2.5 had much less ammonium nitrate than
predicted from the penetration factors for elemental carbon. The indoor gas-phase concentration
of nitric acid was usually lower than outdoors, but the indoor ammonia levels were frequently
higher than outdoors.
The observations of Lunden et al. (2003a) are consistent with the disruption of the NH 4 NO 3 gas/
particle equilibrium as gas-phase nitric acid reacted with the indoor surfaces, causing evaporative
dissociation of aerosol NH 4 NO 3 that originated outdoors. The surfaces took up nitric acid more
readily than ammonia. Lunden et al. showed that the observed evaporation rates for NH 4 NO 3 (0.3
to 18 h −1 ) were in the same range as ventilation rates and higher than particle deposition rates. They
found that the evaporation rate depended strongly on temperature, as well as gas-phase concentra-
tions of ammonia and nitric acid. More detail about the modeling approach for this study is given
in Section 6.5 that follows.
6.4.2 n eutralization oF a cidic P articles
Indoor ammonia provides an example of the occupants' inluence on indoor aerosol chemistry that
was not mentioned in the introduction to this chapter. Humans and their pets generate ammonia that
can neutralize aerosol acidity. Some cleaning products also contribute ammonia. By comparing
ield measurements (Leaderer et al., 1999) with results of environmental chamber studies (Leaderer
et al., 1990) Leaderer et al. found evidence that indoor ammonia neutralized much of the increased
aerosol acidity that originated as sulfur in the fuel of UKHs.
6.4.3 e Mission and P artitioning oF s eMi -v olatile o rganic c oMPounds
As mentioned in Section 6.1, signiicant concentrations of semi-volatile organic constituents of
building materials, furnishings, and consumer products have been reported in indoor air and dust.
Ventilation rate inluences the indoor concentrations of VOCs more than SVOC, whereas concentra-
tions of SVOC are controlled to a greater extent by sorption and (re)emission (Singer et al., 2004).
Increasing attention is being paid to associations between indoor SVOC and respiratory symptoms
(e.g., phthalates: Bornehag et al., 2004). Possible disruptors of human endocrine systems, besides
phthalates, include constituents of textile surface treatments such as perluoroalkyl sulfonamides
(Shoeib et al., 2004) and ire retardants such as PBDEs (Sjödin et al., 2001; Kemmlein et al., 2003)
and triethylphosphate (Carlsson et al., 2000; Salthammer et al., 2003).
In many indoor environments, the gas-phase concentrations of SVOCs can reach supersatura-
tion, and condensation can occur onto walls, windows (Butt et al., 2004), textiles, airborne par-
ticles, air ilters, and even quartz iber ilter sampling media (Mader and Pankow, 2000, 2001a,b;
Weschler, 2003; Xu and Little, 2006). Whereas Figure 6.2 illustrates processes that inluence indoor
aerosol concentrations, Figure 6.10 shows interactions of SVOCs with indoor surfaces, including
emission from furnishings (indoor sources), sorption, desorption, and surface reactions.
As shown in Table 6.7 carpets and walls can function as large reservoirs of semi-volatile com-
pounds such as the plasticizer DEHP that will partition to airborne particles and settled dust.
Partitioning of indoor SVOC to sampling media such as iberglass or quartz ilters (Mader and
Pankow, 2000, 2001a,b) can account for the large positive sampling artifacts that have been
observed for organic carbon concentrations (Landis et al., 2001). Pang et al. (2002) minimized the
indoor positive artifact by removing the gas-phase SVOC before the particles reached the collec-
tion ilter.
Weschler and Nazaroff (2008) examined the factors affecting equilibrium partitioning of SVOCs
to all indoor surfaces, and concluded that equilibrium was reached faster for smaller particles than
for extended surfaces. The authors developed a framework to identify exposure pathways to indoor
SVOCs, in which the rate of equilibration and potential for transport from and to surfaces was