Environmental Engineering Reference
In-Depth Information
generally confined to woods. For thousands of millennia those have been the only
important sources of particulate matter and, besides the comparatively rare excep-
tions represented in the vast majority of cases by some occasional volcanic activ-
ities, the most interesting characteristic for the discussion that follows is constituted
by the particle size: Natural particles are rather coarse.
Taking into account a great variability of dating depending on many factors,
roughly about half a million years ago Man started to be able to light a fire and use
it. That was the start of a no-more natural pollution, but caused by an animal that
had begun to behave in a completely different way from that inborn of all the other
inhabitants of the Planet.
All combustions, without exceptions, produce solid particles whose chemical
composition depends on what is being burnt and on what those chemical elements
find in the environment at the time when the particle is being formed.
As the different technologies grew more and more sophisticated, an increasing
variety of chemicals was introduced in the processing of the products that were
catching on and, as a consequence, particles became more and more complex in
their composition. If for many centuries the phenomenon had a relevance restricted
only to specific environments like, for instance, those of glass blowers or of metal
smelters, the so-called First Industrial Revolution of the Eighteenth Century started
to give it an important impetus, and even more impetus was given about one century
later with the so-called Second Industrial Revolution.
Attaining high temperatures had been a problem for millennia, and that difficulty
was one of the greatest limitations to technical progress. With the widespread,
massive introduction first of coal and later of petroleum as industrial fuels, and with
the technical progresses and inventions of more and more sophisticated machines
that replaced manual labor with a much more effective capacity for work, higher
temperatures could be touched and producing materials, for instance, glass, became
easier and cheaper, and more and more until-then non-existing products could be
fabricated.
Now temperatures far exceeding 10,000
C are easily available at a relatively
low cost with all the benefits they can give but also with a few drawbacks.
As stated above, all combustions generate particles and, as a rule of thumb, the
higher the temperature, the smaller the particles. The importance of this matter of
fact will be described later.
For elementary geometric reasons, if the diameter of a particle is reduced ten
times, its volume and, as a consequence, its mass becomes 1,000 times smaller. A
reduction of diameter of a hundred times implies a mass reduction of one million
times, and so on, since diameter and volumes have a relationship to the third power.
It is anything but common to find in the atmosphere natural solid particles smaller
than 1
m, the usual ones being comparatively bigger. For instance, sand grains can
travel thousands of kilometers as can be seen looking at satellite photographs of
Sahara sand flying at a relative high altitude on the Atlantic Ocean fromWest Africa
as far as the eastern coast of the United States. Smaller particles like the ones
produced by volcanoes can be the cause of important ecological phenomena. A
famous one is the famous “year without a summer”: The 1815 eruption of Mount
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