Environmental Engineering Reference
In-Depth Information
A very good example of nanoparticle sources is the eruption of Krakatoa on
August 27th, 1883. The smoke column reached 80 km in height and the dust thrown
into the ionosphere not only caused strange optical effects visible in North America
and Europe, but also acted as a solar radiation filter, decreasing global temperature
with about 1.5
C in the next 2 years. In addition, the eruption threw a huge amount
of gas into the atmosphere which later air currents carried around the planet, a
phenomenon that led to an unprecedented elevation of acid concentration under the
form of very fine drops in the cirrus clouds at high altitude. Acid rains were the
obvious consequence everywhere in the world [
1
-
7
].
Another example is the Tunguska event [
8
-
11
], whose probable cause was the
collision of a gigantic meteorite or comet fragment with Earth on June 30th, 1908.
For several weeks after the event, luminescent yellowish green clouds that made
reading possible even during moonless nights could be seen above Europe and
North Africa, at the extremity of the troposphere [
12
-
14
].
Some authors [
15
,
16
] hold that the northern lights are very bright optical
phenomena seen on the night sky in the areas near the polar regions, caused by
the interactions between the ionosphere nanoparticles and the solar wind particles,
under the influence of Earth
s magnetic field. In the northern hemisphere, the
phenomenon is known as
aurora borealis
, as Galileo Galilei named it. The northern
lights appear in September-October and March-April. In the southern hemisphere,
aurora australis
was seen for the first time by James Cook, in his failed attempt to
reach the South Pole.
Auroras are not exclusive earthly events. They can also be seen on other planets
of the solar system, such as Jupiter, Saturn, Mars and Venus. Although natural, they
can be reproduced experimentally [
16
].
'
2.2 Volcanic Eruptions
Ash released during volcanic eruptions can reach temperatures over 1,400
C and
has a very complex structure consisting of solid and liquid particulate matter lifted
by the hot gas current [
17
]. Following the paroxysmal phase of the volcano, as the
ash spreads into the atmosphere, gas temperature lowers and gas composition
changes; leading to the accumulation in deposit of particles either clusters through
chemical reactions or based on electrostatic forces of attraction.
Volcanic gas emissions vary with thermodynamic and kinetic conditions (pres-
sure, temperature, speed of reaction and diffusion, etc.) and the nature of magma
(Fig.
2.1
)[
17
]. Most volcanoes on Earth throw basaltic lava and erupt most
frequently along the ocean ridges, at depth, having direct contact with the atmo-
sphere only in several places of the world (Iceland and the Azores for the Atlantic
Ridge).
Basaltic magma is rich in magnesium and iron and poor in silica. It generally has
low viscosity and a reduced gas concentration consisting mainly of carbon dioxide
and sulphur dioxide. Hydrogen sulphide (H
2
S) and hydrochloric acid (HCl) prevail
