Aerosol Chemistry and Physics - Aerosols: Measurement, Dosimetry, and Health Effects - page 131

TABLE 6.1
Mass Flow Rates in Global, Urban, and Indoor Atmospheres

Mass Breathed,
Q a (kg day −1 )

Intake Fraction b
Ratio Q:F Environment Mass (kg) Flow, F (kg day −1 )

Global atmosphere 5 × 10 18 — ∼10 11 —

Urban atmosphere c ∼10 15 ∼3 × 10 15 ∼4 × 10 10 ∼10 −5

Indoor atmosphere d ∼10 12 ∼10 13 ∼8 × 10 10 ∼10 −2

Source: Adapted from Nazaroff, W.W. et al., Atmos. Environ ., 37, 5431, 2003.
a Includes air inside and outside of buildings.
b The descriptor intake fraction was introduced by Bennett et al. (2002).
c Sum of all urban environments (globally).
d Sum of all indoor environments (globally).

atmospheres to the human breathing rate, as shown in Table 6.1. The last column expresses the ratio
of amounts inhaled and amounts emitted as the intake fraction (Bennett et al., 2002). This simple
calculation shows that a nonreactive compound present indoors is about a thousand times more
likely to be inhaled than if the same species is emitted or formed outdoors. Calculations of intake
fractions for PM are the irst steps in incorporating human exposure to PM into life-cycle assessment
of damage to human health. The comprehensive review by Humbert et al. (2011) explains how the
modeling approach incorporates types and source strengths of PM, geography, meteorology, time,
and activity patterns. Hellweg et al. (2009) provide guidance about generating intake fractions for
both gases and PM in the indoor environments. These studies are consistent with one another in
concluding that exposures to outdoor PM are thousands of times higher indoors than outdoors for
the majority of people in the developed world.

6.1.2.2 In the Developed World Roughly Half of Indoor PM Originates Outdoors
In the early 1990s, the Particle Total Exposure Assessment Methodology (PTEAM) study compared
personal exposure to particles smaller than 10 μm in diameter (PM 10 ) in Riverside, California, to
indoor and outdoor concentrations. By using the data to model PM iniltration and removal processes
Ozkaynak et al. (1996) found that over half the indoor particle mass originated outdoors, even in homes
with smoking and cooking. As buildings in the developed world have become tighter (less leaky toward
outdoor air) the outdoor contributions to indoor PM are decreasing somewhat (Mitchell et al., 2007).

6.1.2.3 Personal Cloud Effect Enhances Exposure to PM
The PTEAM study found that personal exposures were higher than exposures based on indoor or
outdoor concentrations (Ozkaynak et al., 1996), and this excess exposure is now called the “personal
cloud.” When Williams et al. (2003a,b) reported PM 2.5 (<2.5 μm in diameter) data from a longitudinal
study, they conirmed the personal cloud effect and found that mean personal PM 2.5 exposures were
only moderately correlated with ambient PM 2.5 concentrations. Liu et al. (2003) also found that
personal exposure exceeded indoor exposure for susceptible populations in Seattle. These studies raise
concerns about the representativeness of central monitoring site data for human exposure assessment.

6.1.2.4 Indoor PM is among the Acute Health Hazards in Homes in the United States
The detailed hazard assessment of contaminants in indoor air by Logue et al. (2010) led to inclusion
of PM 2.5 among the group of acute indoor health hazards, in addition to acrolein, chloroform,
formaldehyde, CO, and NO 2 . Additionally, there is growing recognition that chemical and physical
changes in indoor air can contribute to increased exposure to irritants and inlammatory agents
(Mitchell et al., 2007). For example, the aerosol-producing reactions of low levels of iniltrated