Mechanisms of Nanoparticle Formation and Reformation in the Atmosphere - Nanoparticles' Promises and Risks - page 57

4.3 Oxides and Salts

The first source of oxide nanoparticles in the atmosphere is particulate resulted from
waste heaps of oxide ore flotation plants or slag left over after ferrous and
non-ferrous metallurgical processing. Secondary sources are the industrial coal
combustion plants, mainly the flying ash, and the waste incineration plants that
produce oxides through the flame oxidation of fusible metals at temperatures below
1,000 C[ 16 - 18 ]:

Sn þ O 2 ! SnO 2 ð 4 : 13 Þ

2Hg þ O 2 ! 2HgO ð 4 : 14 Þ

2Zn þ O 2 ! 2ZnO ð 4 : 15 Þ

Pb þ O 2 ! PbO 2 ð 4 : 16 Þ

At nanoparticle level, ammonium salts are easily produced and represent the
main constituents of smog (urban aerosols) which affects atmospheric opacity and
increases the Earth s greenhouse effect.

'

NH 3 þ H 2 SO 4 ! NH 4 HSO 4 ð 4 : 17 Þ

NH 4 HSO 4 þ NH 3 ! ð NH 4 Þ 2 SO 4 ð 4 : 18 Þ

NH 3 þ HNO 3 ! NH 4 NO 3 ð 4 : 19 Þ

NH 3 þ HCl ! NH 4 Cl ð 4 : 20 Þ

Combined with acids present in the atmosphere through the series of reactions
described above, very finely divided salts form metallic cations that occur in
nanoparticles resulting from waste heaps or slag. Depending on salt density, wind
speed and humidity, one can find, at various altitudes, almost all nitrates, sulphates
and chlorides formed with the cations (in different oxidation states) of elements
with stable isotopes or very long half-lives included in the periodic table [ 19 ]:

Me nþ þ n HNO 3 ! Me NO 3 ð Þ n þ n = 2H 2 ð 4 : 21 Þ

Me nþ þ

n H 2 SO 4 ! Me 2 SO 4 ð Þ n þ n H 2 ð 4 : 22 Þ

Me nþ þ n HCl ! MeCl n þ n = 2H 2 ð 4 : 23 Þ

The data provided in this subsection show that nanoparticles tend to form
constantly, as new amounts of materials derived from anthropogenic or natural
activities (volcanic eruptions, cosmic dust, desert dust) rise in the atmosphere.
These materials interact with one another or with the gaseous constituents in the
air, but they also contribute to nanoparticle reformation through opposed tendencies
of sedimentation/de-sedimentation, changes in their chemical nature and/or their
previous state of matter.