Health Effects of Aerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 566

(Table 23.1).* Speciically omitted are radioactive aerosols, aerosols encountered in industrial envi-
ronments, and medical and pharmaceutical aerosols.
Broadly, the health-relevant aerosols to be considered can be classiied as those derived from the
activities of man (e.g., combustion of fuels) and those that occur in natural environments (e.g., bio-
aerosols) or as the result of natural processes (e.g., windblown dusts that carry man-made products
such as pesticides or bioaerosols such as soil-resident fungal spores).
23.2 CHARACTERISTICS OF OUTDOOR (AMBIENT) AND INDOOR
AEROSOL SOURCES OF IMPORTANCE TO HUMAN HEALTH
Clearly, the activities of people can modify the distribution and the concentrations of aerosol com-
ponents that would exist in nature even in the absence of human activity. Humans come into con-
tact with these aerosols both indoors and outdoors. Components of outdoor aerosols iniltrate into
indoor environments to varying degrees, but, with the exception of products of indoor combustion
(e.g., ireplaces, biomass burning stoves), indoor sources are not usually important contributors to
the outdoor aerosol.
23.2.1 o utdoor a erosol (t able 23.1, F igure 23.1)
The typical outdoor aerosol can be described conveniently in terms of three components.
Combustion-generated particulate matter (PM) is the source for the vast majority of PM ≤1 μm
(aerodynamic diameter), and these particles are the target of federal and state clean air criteria.
With regard to human health, the particle size distribution observed for PM ≤1 μm has implica-
tions for the deposition distribution within the respiratory tract and toxicological properties that
are related to surface area characteristics independent of the toxicology of the speciic compo-
sition of the particle (e.g., see Ref. [1]). The relationship between particle size, deposition, and
surface area is shown in Figure 23.2, and the implications for toxicology will be discussed in a
later section. The chemical composition of the combustion-related aerosol is complex, and its
exact composition depends on the mix of sources that contribute to it (Table 23.1; primary source
contributions and long-range transport), meteorological conditions, and large-scale regional
variations.
The so-called coarse component of the outdoor aerosol is deined in various ways. In the con-
text of U.S. National Ambient Air Quality Standards (NAAQS), the classiication of “coarse” is
reserved for PM between 2.5 and 10 μm aerodynamic diameter (see Vol. I of Ref. [2]). However,
given the substantial differences in sources and deposition properties and contribution to overall
surface area (Figure 23.2), the classiication based on a cut point of 1 μm seems more useful
for health assessment. As noted in Figure 23.2, there is a small overlap of sources and particle
modes, which is related to cut-point characteristics of the sampling devices and conditions dur-
ing sampling particle agglomeration and to meteorological factors such as high winds (see Vol. I
of Ref. [2]). Among the components of coarse PM, the bioaerosol has considerable implications
for human health. Plant pollens have long been known to be important triggers of allergic reac-
tions. However, more recently, the importance of fungal spores and toxins (e.g., see Refs [3-5])
and bacterial products, especially endotoxins (e.g., see Refs [6,7]), has been recognized. Recent
studies have suggested that a major contributor of the toxicological and inlammatory potential
of PM is related to bacterial endotoxins, and this activity is found almost exclusively in the
PM 10-2.5 of mass distribution [6-9].
* Chapter 20 presents detailed information about the relevant aspects of the bioaerosol and some data on health effects.
This chapter will focus on disease-speciic health effects based on epidemiological and clinical data.