Basics and Discovery of Atmospheric Chemicals - Air Pollution and Global Warming: History, Science, and Solutions - page 21

the Mediterranean Sea. Bromine means “stench” in
Greek. It is a heavy, reddish-brown liquid that evap-
orates at room temperature to a red gas that irritates the
throat and eyes and has a strong smell. It is the only
nonmetallic element that can be in the liquid phase at
room temperature. Balard also discovered hypochlor-
ous acid HOCl(g)]. Bromine and hypochlorous acid
contribute to ozone destruction in the upper atmosphere
today.

1785, he had not associated the odor with a gas in the
air. In 1840, Schonbein proposed that the odor he found
was due to a distinct chemical. In an 1841 report to the
British Association for the Advancement of Science, he
further wrote:

The peculiar smell makes its appearance as soon as the
electrolysis of water begins and continues to be per-
ceived for some time after stopping the flow of elec-
tricity. . . . The odor must be due to some gaseous sub-
stance disengaged (conjointly with oxygen) from the
fluid due to the decomposing power of the current.

1.2.3.4. Ozone (Gas)
On March 13, 1839, the German chemist Christian
Friederich Schonbein (1799-1868; Figure 1.22) dis-
covered one of the most important atmospheric trace
gases, ozone [O 3 (g)]. He discovered ozone by pass-
ing an electric current through water (electrolysis). The
resulting gas had a pungent, sweet smell, and he named
it ozone after the Greek word, “ozein,” which means
“to smell.” Although the Dutch chemist Martinus Van
Marum (1750-1837) had previously detected “the odor
of electrical matter” associated with electrical sparks in

In 1845, the Swiss scientists Auguste de la Rive
(1801-1873) and Jean-Charles de Marignac (1817-
1894) suggested that ozone is a form of oxygen. How-
ever, only in 1865 did Swiss chemist Jacques-Louis
Soret (1827-1890) identify the structure and molecular
formula of ozone as O 3 .In1879, the French physi-
cist Alfred Cornu (1841-1902) found a sharp cutoff in
the ultraviolet light spectrum reaching the Earth's sur-
face. In 1881, Walter N. Hartley explained the cutoff
as due to absorption of short ultraviolet wavelengths by
ozone high in the atmosphere. In 1913, French physi-
cists Charles Fabry (1867-1945) and Henri Buisson
(1873-1944) quantified the thickness of this layer of
ozone in the upper atmosphere, which is now referred
to as the stratospheric ozone layer .
In 1846, Schonbein also discovered guncotton ,the
first nitro-based explosive and precursor to trinitro-
toluene (TNT). Nitro-based explosives were smokeless.
Previously, gunpowder, a black powder mixture of sul-
fur, charcoal, and saltpeter (potassium nitrate) was the
explosive and gun propellant of choice, but it resulted
in poor battlefield visibility. Schonbein discovered gun-
cotton after spilling nitric acid and sulfuric acid on his
kitchen counter, and then wiping up the mess with his
wife's cotton apron. After hanging the apron to dry
overthe stove, it readily caught fire. The nitric acid had
reacted with the cellulose in the cotton to form explo-
sive nitrocellulose and water. The sulfuric acid absorbed
the water, preventing the water from diluting the nitric
acid. Because guncotton was so dangerous to handle,
factories producing it tended to explode, so it was not
widely used on its own. In 1889, it was used more safely
in a mixture called cordite, which contained guncotton,
nitroglycerine, and Vaseline in long cords.

1.2.3.5. Noble Gases
The air contains several inert noble gases in trace quan-
tities, including helium (He), argon (Ar), neon (Ne),

Figure 1.22. Christian Friederich Sch onbein
(1799-1868). Edgar Fahs Smith Collection, University
of Pennsylvania Library.