Environmental Engineering Reference
In-Depth Information
2HBr
þ
3O
2
!
2HBrO
3
ð
2
:
3
Þ
There is little information about the hydrofluoric acid concentration eliminated
by volcanoes in the atmosphere. In some cases (Laki 1783 or Mount Hudson 1990),
hydrofluoric acid emissions were very high and contaminated the vegetation,
killing animals and people. As with the other halogen acids, hydrofluoric acid
spreads around the volcanoes through acid rains, so that excessive fluoride ions
are one of the major causes of animal mortality on large areas, even a long time
after the eruption. Fluoride intoxication becomes chronic and eventually lethal, if
its concentration in the freshly grown vegetal matter exceeds 250 ppm [
24
].
The chemical composition of forming ash is easily identified if one studies the
permanent emissions of latent volcanoes.
Dry fumaroles lack water and their temperature exceeds the critical temperature
of water (374
C). They contain nitrogen (N
2
), carbon oxide (CO), hydrogen (H
2
),
methane (CH
4
), and sodium chloride vapour (NaCl), potassium chloride (KCl) and
copper oxide (CuO). Through deposition on the edge of the crater, on the surface of
the bombs thrown during eruption or under the form of ash, fumaroles generate
particulate matter of halite (NaCl), sylvite (KCl), and tenorite (CuO) [
17
].
Acid fumaroles consist of hydrogen sulphide (H
2
S), sulphur dioxide (SO
2
),
carbon dioxide (CO
2
) and water vapour. Their temperature is close to the critical
temperature of water. They also contain iron chlorides (FeCl
2
, FeCl
3
), copper
chlorides (CuCl, CuCl
2
) or iron oxides, mostly magnetite (Fe
2
O
3
), if acidity is
not very high. In the presence of hydrogen sulphide (especially in submarine
fumaroles), iron is found under the form of marcasite and pyrite (FeS, FeS
2
)[
17
].
Alkaline fumaroles are made of ammonium chloride (NH
4
Cl), ammonium
hydroxide (NH
4
OH), in the presence of ammonia (NH
3
), in contact with water
vapour. Ammonium chloride takes the form of micrometre or sub-micrometre
particles. The temperature of these fumaroles is 100-400
C.
Solfataras is a natural volcanic steam vent in which sulphur gases are the
dominant constituent along with hot water vapours. The fumaroles releasing
gases contain sulphur, hydrosulphuric acid (H
2
S) and or sulphur dioxide (SO
2
)
and, in the presence of water vapour, sulphurous acid (H
2
SO
3
) and sulphuric acid
(H
2
SO
4
), the latter being more stable. Realgar, orpiment (As
2
S
3
), ferrous, and
copper pyrites, iron sulphate (FeSO
4
) and native sulphur resulted from vapour
condensation have been identified as solid state of matter [
17
].
It must be specified that most metal and non-metal ores in Earth
s crust were
formed throughout the geological eras, because of volcanic activity. Consequently,
any chemical element existing as such or in one of its combinations may be found in
the atmosphere under the form of nanoparticles during eruptions or immediately
after them.
'
