Aerosol Chemistry and Physics - Aerosols: Measurement, Dosimetry, and Health Effects - page 160

(Weschler, 2011). Weschler and Shields (1997) showed that indoor aerosol generation was possible
when unsaturated hydrocarbons react with ozone under typical building airlows and residence
times. In 1999, they provided the irst experimental evidence for the counterintuitive notion that
ine particles are produced indoors by cleaning practices that residents often consider protective
and health promoting. Using a pair of matched ofices with the same ambient ozone concentra-
tions and ventilation rates, they tracked increased numbers of ine particles in a room into which
d-limonene had been released (Weschler and Shields, 1999; Weschler 2000). Limonene is a bio-
genic terpenoid, a cyclic alkene found in lemon and pine oils that are common components of
cleaning products. Shaughnessy et al. (2001) compared the reactivity of hydrocarbons found in
SHS with ozone and showed that both limonene and dimethylfuran in SHS would react with 50
ppb ozone indoors even at higher than typical residential air exchange rates. Several recent studies
have investigated the inluence of air exchange rates on indoor aerosol generation from reactions of
unsaturated hydrocarbons. Sorenson and Weschler (2002) applied computational luid dynamics;
Weschler and Shields (2003) showed how the new particle number and size distributions depended
on air exchange rates. Sarwar et al. (2003) extended the work to predict how indoor secondary
aerosol formation depends not only on ventilation rates, but also building temperature, indoor
terpene emission rates, as well as outdoor ozone and particle concentrations. A review by Nazaroff
and Weschler (2004) summarized the available data on reaction rates of terpenes and related com-
pounds with ozone, OH, and nitrate radical. Mixing ozone with the vapor emissions of common
household products and with air freshener emissions in a laboratory chamber experiment led to
the formation of an initially large number of UFP that subsequently grew by condensation and
agglomeration (Destaillats et al., 2006a). Experimental factors such as the air exchange rate, the
RH, and the presence of seed particles had a strong inluence in the observed particle dynamics
(Coleman et al., 2008).
In parallel with the explosion of work on indoor secondary aerosol formation, rapid progress
is occurring in the identiication of reaction mechanisms for the oxidation of terpenoids by ozone.
Figure 6.11, kindly provided by P. Ziemann, shows a condensed version of the likely reaction path-
way for generation of the products that are shown in Figure 6.12, which is based on the work of Yu
et al. (1999). While ozone/terpenoid chemistry is considered the most signiicant chemical source
of indoor aerosols, more recently other systems have been studied. For example, Sleiman et al.
(2010a) described the formation of UFP in the reaction of ozone with nicotine vapor, as well as with
constituents of secondhand tobacco smoke (that included nicotine).
6.4.5 M ultiMedia M odeling For tHe i ndoor e nvironMent
Bennett and Furtaw (2004) introduced the use of fugacity, the tendency of pollutants to escape from
an environmental compartment to another, as a promising approach for exploring indoor chemical
and physical process. The upper part of Figure 6.13 shows a home loor plan from their study of the
behavior of pesticides. The lower part shows a corresponding diagram that highlights multimedia
processes indoors. This type of multimedia model has been successfully used to understand the fate
and transport of pollutants as they move among outdoor environmental “compartments” (soil, sedi-
ments, water, and air) (Cowan et al., 1995). Such a framework shows promise for clarifying the role
of indoor aerosol chemistry in human exposure to toxic and hazardous pollutants, and it builds on
the mass balance approach described in Section 6.5.
6.5 FATE AND TRANSPORT
The concentration of aerosols indoors is the result of several dynamic processes where the production
of aerosols (source terms) is balanced by various removal or transformation mechanisms. These
processes were shown schematically in Figure 6.2.