Environmental Engineering Reference
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10,000
Philadelphia
1,000
100
Total
Coarse mode
10
Intermediate mode
Accumulation mode
1
1
10
100
1,000
10,000
(a)
Days of exposure
10
Philadelphia
1
0.1
Total
Intermediate mode
Coarse mode
0.01
Accumulation mode
0.001
0.001
0.01
0.1
1
10
100
(b)
Age in years
FIGURE 23.13
(a) Particle mass retained in the lung versus days of exposure, predicted by [322] for expo-
sure to Philadelphia aerosol, under the assumption of dissolution absorption half-times of 10, 100, 1000 days
for three modes of particles. (b) Same data converted to speciic lung burden, based on continuous exposure
to Philadelphia aerosol at 50 μg/m
3
. (Adapted from U.S. Environmental Protection Agency (EPA), Air qual-
ity criteria for particulate matter Volume II, in Air Quality Criteria for Particulate Matter, Volumes I-III,
EPA/600/P-95-001bF, National Center for Environmental Assessment Ofice of Research and Development,
U.S. EPA, Washington, DC, 1996, Figures 10.55, 10.56.)
different modes. Given the importance of exposures at critical points of human development, this
type of heterogeneity of accumulation may have important implications for health effects related to
chronic exposures to indoor and outdoor aerosols.
23.4 MECHANISMS OF TOXICITY OF AEROSOL COMPONENTS
The mechanisms that underlie the effects of the nonbiological ambient and indoor aerosols and
the biological components of the aerosols have a number of features in common. Both compo-
nents directly trigger inlammatory responses and/or trigger (directly or indirectly) immunological
responses that lead to speciic inlammatory responses that characterize various allergic pheno-
types (e.g., asthma allergic rhinitis/conjunctivitis). Reactive oxygen and nitrogen species are major
products of inlammatory reactions [34,35] and can be generated by neutrophils, macrophages, and
eosinophils in response to contact (ingestion) with biological materials [36] or ambient particles
[37]. Moreover, the organic carbon and transition metal components of ambient and indoor aerosol
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