Environmental Engineering Reference
In-Depth Information
ozone with terpenes (from cleaning products, air fresheners, and fragrances) are associated with
increased sensory irritation (Wolkoff et al., 2006). Another example, a review of ive studies by
Mølhave (2008), concluded that indoor dust can lead to inlammatory and allergic responses in
ofice workers at levels that occur episodically.
6.1.2.5  Introduction to Characterization of Indoor Aerosols
With growing attention to the health effects of inhaled particles, more and more attention has been
directed at characterizing indoor aerosols. The growing use of continuous monitors for both ine
and ultraine particles (UFP) has improved the understanding of iniltration of ambient PM and the
dynamic behavior of indoor sources of PM (Wallace, 2006; Wallace et al., 2006). Many of the stud-
ies cited in the following would not have been possible without the sampling methods and types of
instrumentation that have been validated and used indoors by Wallace et al. (2011), among others.
6.1.2.5.1 PM 2.5
The U.S. EPA has set National Ambient Air Quality Standards (NAAQS) for ambient PM 2.5 at
15 and 35 μg m −3 and for annual and daily averages, respectively. In long-term ield studies in
residences, Wallace, 2006 and Wallace et al. (2006) showed that typical indoor activities like
cooking, cleaning, and personal care frequently raised PM 2.5 concentrations above the NAAQS
daily standard. The review of indoor pollutants by Logue et al. (2011) found that the mean indoor
PM 2.5 concentration was 16 μg m −3 from 13 studies of homes in the United States and other
similar industrialized countries. The 25th, 75th, and 90th percentiles were 9, 20, and 86 μg m −3 ,
respectively. Average PM 2.5 levels were much lower than outdoors in buildings such as ofices
and schools that iltered ambient air through mechanical ventilation systems, except when human
activities generated both ine and coarse PM (Parker et al., 2008).
6.1.2.5.2 Ultraine Particles
Particles below 100 nm in diameter are typically referred to as UFP, and exposure to them has been
increasingly linked to damage to human health (Knol et al., 2009 and included citations). Exposure
to outdoor UFP typically occurs when people are near fresh smog or combustion sources like vehi-
cles. After emission, UFP decay faster than PM 2.5 because they quickly agglomerate with each other,
accrete to PM 2.5 or interact with surfaces. Because of their size they usually do not contribute much to
PM 2.5 mass. With the advent of improved instruments like water-based condensation nucleus counters,
researchers have been monitoring number concentrations of UFP down to 6 nm in several types of
indoor environments, with emphasis on determining what fractions of indoor UFP originated outdoors
and how much indoor UFP is generated by typical human activities, over what timescales. A recent
pair of articles by Bhangar et al. (2011) and Mullen et al. (2011) included useful citations to the small
but growing literature on the characterization of UFP in both outdoor and indoor environments Their
studies focused on UFP in seven California homes and six schools, respectively. The mean exposure
concentration to the residents of the seven homes was 17 × 10 3 cm −3 over the time they were at home,
with 40% of exposure at home due to iniltrated UFP and the remainder from episodic generation of
UFP indoors (Bhangar et al., 2011). Particle number concentrations were about the same in the schools,
but most of the indoor UFP came from outdoor sources (Mullen et al., 2011). From wintertime mea-
surements of ive homes in northern New York State, McAuley et al. (2010) found that indoor/outdoor
ratios averaged 0.3 for UFP when the only indoor aerosol source was iniltrated PM from trafic.
6.1.3 
o utdoor  P articles
6.1.3.1  Composition PM 2.5  in the United States
Since roughly one-third to half of PM in homes has iniltrated from outdoors (e.g., Wallace et al.,
2003), an overview of outdoor PM composition provides a useful starting point for investigation of
indoor aerosol chemistry. Figure 6.1 shows the four-season average PM 2.5 concentrations for urban
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