Page 301 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

286 Principles and Methods

aggregation and deposition are directly applicable to atmospheric par-
ticles. However, the origins and characteristics of particles in air and
water may differ. Due to the importance of combustion as a source of
exposure to nanoscale particles, and the potential similarity between
soot and fullerenes, we briefly address this aspect.
Atmospheric nanoparticles may be detected and characterized by
simultaneously measuring the light scattering, the photoelectric charg-
ing, and the diffusion charging [114]. These methods may also be used
to determine the likely source of the nanoparticles and differentiate
between those from combustion processes and background nanoparti-
cles. Particles carrying polycyclic aromatic hydrocarbons are detected
by their large photoelectric charging signature, whereas particles from
other sources only exhibit light scattering and diffusion charging.
Although carbon nanotubes have not yet been detected as unintentional
combustion products, C 60 maybe present in some cases.
Nanoscale particles may be produced and dispersed in the atmos-
phere through both natural processes and human activities. A signifi-
cant source of manmade nanoscale particles is the burning of
hydrocarbon fuels such as diesel, gasoline, and propane [113, 115].
Industrial processes are another source of atmospheric nanoparticles,
though their contribution is far less than that of vehicle exhaust. Thus,
relatively high concentrations of these nanoparticles occur along road-
sides and other areas immediately surrounding combustion sources [113].
Nanoscale particles formed from the burning of these fuels generally fall
in a size range of 10 to 60 nm [113, 116] and are primarily composed of
unburned oils, polycyclic aromatic hydrocarbons, inorganic compounds,
and sulfates [115, 116]. The composition and properties of the airborne
nanoparticles will vary according to the type of fuel and engine that is
used (Table 7.3) [115, 116]. For instance, gasoline engines tend to pro-
duce smaller sized nanoparticles while diesel engines emit larger
agglomerates in a size range of 50 to 1000 nm. Similar to nanoparticles
in aqueous media, the behavior and properties of atmospheric nanopar-
ticles are dynamic [113, 116].

TABLE 7.3 General Composition of Nanoparticles Emitted from Diesel and Gasoline
Engines [116]. Particles in Diesel and Gasoline Exhaust at the Point of Emission Are
Generally Smaller than 50 nm, with Diesel Exhaust also Containing Some Larger
Particles up to 1000 nm in Diameter.
Diesel exhaust Gasoline exhaust
Carbon Black 68% 32%
Organic Carbon 31% 61%
Other Materials 1% 7%