Environmental Engineering Reference
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(residential or school distance from roadway and markers of vehicle combustion [black smoke as a
surrogate for elemental carbon, NO 2 in the absence of ixed sources]) and the increased occurrence
of respiratory symptoms in children, decreased lung function in children, and increased mortality
across all ages. In many of the studies, the methods of exposure assessment are somewhat crude
(many do not even take location of school or residence in relation to predominant wind direction)
and the choice of health outcomes is of variable quality; nonetheless, the fact that distance from
roadways has the most consistent association with health outcomes adds some coherence to a causal
association [143]. Figure 23.18 shows the decay of black carbon as a marker of diesel exhaust from
two freeways with different diesel vehicle loads in southern California [144]. At a distance between
80 and 150 m from the roadway (dependent on vehicle road), the levels of black carbon return to
background. Given the diversity of methods of exposure assignment and types of health outcomes,
only a qualitative conclusion is reasonable: that is, there is a strong association between exposure to
trafic sources of ambient PM and a variety of health outcomes.
Indoor combustion sources : As noted earlier, indoor environments of a variety of types (home,
work, vehicles) are important sources of anthropogenic PM aerosol in both developed [11,18,145]
and developing countries [146]. No further comment is made with regard to human health effects
that are attributable to indoor combustion sources, since in general they do not differ qualitatively
from those that would be related to outdoor sources. The major issue in this regard is the relative
contribution of indoor and outdoor sources to the overall burden of PM aerosol experienced by
humans. A full discussion of this is beyond the scope of this chapter (see Refs [10,146,147]. The
health effects related to secondhand exposure to cigarette smoke have been reviewed recently by the
National Cancer Institute [148] and an update will appear in a new report of the Surgeon General of
the United States that has not yet been released.
Bioaerosols : Human health effects related to bioaerosols have been discussed briely in Chapter
14 and the mechanisms for the noninfectious components of PM aerosols have been discussed
earlier.
Endotoxins are of particular interest, since they are ubiquitous in the environment either adsorbed
onto the surfaces of particles generated through combustion processes (refer to earlier text) or as
part of indoor dust created by human activity and tracking of soil into homes and the presence of
25
20
15
710 freeway (diesel >25%)
R 2 = 0.99
y = 6.2 + 40.8 exp(−0.074x)
405 freeway (diesel <5%)
R 2 = 0.99
y = 1.32 + 7.79 exp(−0.022x)
10
5
0
0
100
200
300
Distance from freeways (m)
FIGURE  23.18  Decay of black carbon concentrations as a function of distance from two freeways
in southern California with different loads of diesel vehicle trafic. (From Zhu, Y. et al., Atmos. Environ .,
36, 4375, 2002.)
 
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