Geoscience Reference
In-Depth Information
soil dust plumes originating from the Sahara Desert.
Soil dust also enters the air when off-road and agri-
cultural vehicles drive over loose soil or when on-road
vehicles resuspend soil dust. Additional dust is resus-
pended during construction or demolition. Fifty percent
of all soil dust emitted may be due to anthropogenic
activities (Tegen et al., 1996).
top of the plume. Volcanic magma also contains carbon
dioxide [CO
2
(g)], sulfur dioxide [SO
2
(g)], carbonyl sul-
fide [OCS(g)], and molecular nitrogen [N
2
(g)]. Lesser
gases include carbon monoxide [CO(g)], molecular
hydrogen [H
2
(g)], molecular sulfur [S
2
(g)], hydrochlo-
ric acid [HCl(g)], molecular chlorine [Cl
2
(g)], and
molecular fluorine [F
2
(g)].
Vo lcanos emit particles that contain the elements of
the Earth's mantle (e.g., Table 2.2). The most abun-
dant particle components in volcanic eruptions are sil-
icate minerals (minerals containing Si). Emitted vol-
canic particles range in diameter from smaller than 0.1
5.2.1.3. Volcanic Eruptions
The word
volcano
originates from the ancient Roman
god of fire
Vulcan
,afterwhom the Romans named an
active volcano,
Vulcano
.Today, more than 500 vol-
canos are active on the Earth's surface. Volcanos result
from the sudden release of gases dissolved in magma,
which contains 1 to 4 percent gas by mass. Water vapor
is the most abundant gas in magma, comprising 50
to 80 percent of its mass. Figure 5.4, showing emis-
sions from the Sarychev Volcano, indicates that some
of the fast-rising water vapor (in the form of steam)
from the volcano expands and cools to form a cloud on
mtolarger than 100
m. As seen in Table 5.4, parti-
cles 100
mindiameter take 1.1 hours to fall 1 km by
sedimentation. The only volcanic particles that survive
more than a few months before falling to the ground
are those smaller than 4
m. Such particles require
at least 23 days to fall 1 km. Larger volcanic parti-
cles fall to the ground more quickly. Volcanic particles
of most sizes are removed more readily by rain than
by sedimentation and contain the components listed in
Table 5.2.
Vo lcanic gases such as carbonyl sulfide [OCS(g)] and
sulfur dioxide [SO
2
(g)] are sources of new particles.
When OCS(g) is injected volcanically into the strato-
sphere, some of it photolyzes, and its products react to
form SO
2
(g), which oxidizes to gas-phase sulfuric acid
[H
2
SO
4
(g)], which then nucleates to form new sulfuric
acid-water aerosol particles. A layer of such particles,
called the
Junge layer
, has formed in the stratosphere
by this mechanism (Junge, 1961). The average diam-
eter of these particles is 0.14
m. Sulfuric acid is the
dominant particle constituent, aside from liquid water,
in the stratosphere and upper troposphere. More than 97
percent of particles in the lower stratosphere and 91 to
94 percent of particles in the upper troposphere contain
oxygen and sulfur in detectable quantities (Sheridan
et al., 1994).
5.2.1.4. Biomass Burning
Biomass burning
is the burning of evergreen forests,
deciduous forests, woodlands, grassland, and agricul-
tural land, either to clear land for other use, stimulate
grass growth, manage forest growth, or satisfy a rit-
ual. Biomass fires are responsible for a large portion of
particle emissions. Such fires may be natural or anthro-
pogenic in origin. Figure 5.5 shows a savannah fire in
Kenya.
Biomass burning produces gases, such as CO
2
(g),
CO(g), CH
4
(g), NO
x
(g), and ROGs, and particles,
Figure 5.4.
Eruption of Sarychev Volcano, Kuril
Islands, northeast of Japan on June 12, 2009. The
satellite image from the International Space Station
indicates a cloud forming on top of the plume due to
condensation of rapidly rising and cooling hot water
vapor. The volcano punched a hole through a
stratiform cloud deck due to the heat emanating out
from the eruption. Image courtesy of Earth Sciences
and Image Analysis Laboratory, NASA Johnson
Space Center, ISS020-E-9048.JPG, http://eol.jsc.nasa
.gov.
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