Geoscience Reference
In-Depth Information
Table 5.6.
Dominant sources and components of nucleation, accumulation, and coarse mode particles
Nucleation mode
Accumulation mode
Coarse mode
Homogeneous nucleation
Industrial emissions
Sea spray emissions
H
2
O(aq), SO
4
2
−
,NH
4
+
H
2
O(aq), Na
+
,Ca
2
+
,Mg
2
+
,K
+
,
Cl
−
,SO
4
2
−
,Br
−
,POM
BC, POM, Fe, Al, S, P, Mn, Zn,
Pb, Ba, Sr, V, Cd, Cu, Co, Hg, Sb,
As, Sn, Ni, Cr, H
2
O(aq), NH
4
+
,
Na
+
,Ca
2
+
,K
+
,SO
4
2
−
,NO
3
−
,
Cl
−
,CO
3
2
−
Fossil fuel emissions
Fossil fuel emissions
Soil dust emissions
BC, POM, SO
4
2
−
,Fe,Zn
BC, POM, SO
4
2
−
,Fe,Zn
Si,Al,Fe,Ti,P,Mn,Co,Ni,Cr,
Na
+
,Ca
2
+
,Mg
2
+
,K
+
,SO
4
2
−
,
Cl
−
,CO
3
2
−
,POM
Biomass- and biofuel-burning
emissions
Biomass- and biofuel-burning
emissions
Biomass- and biofuel-burning ash,
industrial fly ash, tire particle
emissions, pollen, spores, bacteria,
viruses
BC, POM, K
+
,Na
+
,Ca
2
+
,Mg
2
+
,
SO
4
2
−
,NO
3
−
,Cl
−
,Fe,Mn,Zn,Pb,
V, C d , C u , Co, Sb, As,Ni,Cr
BC, POM, K
+
,Na
+
,Ca
2
+
,Mg
2
+
,
SO
4
2
−
,NO
3
−
,Cl
−
,Fe,Mn,Zn,
Pb, V, Cd, Cu,Co,Sb,As,Ni,Cr
Condensation/dissolution
Condensation/dissolution
Condensation/dissolution
H
2
O(aq), SO
4
2
−
,NH
4
+
,POM
H
2
O(aq), SO
4
2
−
,NH
4
+
,POM
H
2
O(aq), NO
3
−
Coagulation of all components
from nucleation mode
Coagulation of all components
from smaller modes
is hygroscopic, it absorbs liquid water at high relative
humidity and becomes spherical. If ions are present
and the relative humidity decreases, crystals may form
within the particle. Some observed aerosol particles are
flat, others are globular or contain layers, and still others
are fibrous.
Of particular interest is the morphology and shape of
soot particles, which contain BC, POM, O, N, and H.
They also have important optical effects. The only atmo-
spheric source of soot is emissions. The main combus-
tion sources of soot are fossil fuel, biofuel, and biomass
burning. An emitted soot particle is irregularly shaped
and mostly solid, containing from 30 to 2,000 graphitic
spherules aggregated with random orientation by colli-
sion during combustion (Katrlnak et al., 1993). Figure
5.16b shows an example of a soot aggregate.
Once emitted, soot particles can coagulate or grow.
Because soot particles are porous and have a large
surface area, they serve as sites on which conden-
sation occurs. Although BC in soot is hydrophobic,
some organics in soot attract water, in which inor-
ganic gases dissolve (Andrews and Larson, 1993). Evi-
dence of soot growth is abundant because traffic tunnel
studies (Venkataraman et al., 1994) and test vehicle
Figure 5.16.
Transmission electron microscopy
images of (a) ammonium sulfate particles containing
soot (arrows point to soot inclusions), (b) a chainlike
soot aggregate, and (c) fly ash spheres consisting of
amorphous silica collected from a polluted marine
boundary layer in the North Atlantic Ocean. From
P osfai et al. (1999).
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