Chemistry Reference
In-Depth Information
the lower stratosphere while the temperature drops
to -80°C. Clouds of fine HNO
3
·3H
2
O particles form
and their surfaces facilitate reaction of the reservoir
chlorine species to form chlorine molecules:
The use of radon trapping below buildings and
frequent air changes to sweep the gas and its decay
products away can control the hazard. An action
level of 200 Bq m
-3
has been proposed by the
National Radiological Protection Board.
HCl + ClONO
2
Æ Cl
2
+ HNO
3
When the sunlight returns, photolysis resumes and
a pulse of Cl
•
is generated:
Cl
2
UV
Asbestos and other inorganics
Asbestos is the name for a group of natural fibrous
minerals whose inertness and inflammability led to
widespread use as insulating materials and vehicle
brake linings. However, the fibres readily become
airborne and, once inhaled, reside in the lungs for
decades leading to irritation and eventually to
disease (asbestosis).
Other inorganic substances that can become work-
place pollutants of concern include compounds of
arsenic, beryllium, cadmium, chromium (VI), nickel
carbonyl and subsulfide, selenium sulfide, carbon
monoxide and nitrogen dioxide.
Particles less than 10 mm in diameter, whatever
their composition, may produce respiratory irritation
or allergic response and provide a pathway to the
lungs and hence the bloodstream for a wide range
of non-volatile toxins that may become suspended
through mechanical or heating operations.
Cl
•
+ Cl
•
Other halogens also contribute to ozone depletion.
Bromine species from methyl bromide derived from
soil fumigation, biomass burning, leaded petrol and
halon fire suppressants are particularly potent.
The UN Convention on Protection of the Ozone
Layer (Vienna Convention, 1985) set in place poli-
cies that began the process of reducing ozone-
depleting chemicals in the stratosphere. The use of
hydrochloroflurocarbons (which have shorter life-
times in the troposphere) as substitutes for CFCs has
assisted in this.
2.4 Pollution of the built environment
'Get your room full of good air, then shut up the
windows and keep it. It will last for years.'
Stephen Leacock (1869-1944)
Indoor air, both industrial and domestic, contains a
complex mixture of thousands of chemical species,
especially if cigarette smoke is present. Concentra-
tions of toxic and carcinogenic substances are likely
to be higher indoors than out, especially in industrial
environments. The major groups of concern are:
radon, asbestos, other inorganics, organic com-
pounds and particulates.
Organic compounds
Organic compounds of particular concern for the
indoor environment, which are known or suspected
carcinogens, include benzene,
p
-dichlorobenzene,
carbon tetrachloride, chloroform, methylene chlo-
ride, formaldehyde and PAHs.
3 Chemistry of the Terrestrial Environment
Radon
Radon is produced by the decay of uranium or
thorium isotopes in the rocks, soils and building
materials. It is a gas that diffuses through fissures and
accumulates in air spaces such as mines, factories
and houses. It has a short half-life (Rn-222 = 3.82
days), decaying to alpha-emitting isotopes of lead
and polonium (Pb-210, Po-210, Po-214, Po-218).
These are solids and adhere to particles in the air that
are inhaled and lodge in the lungs. They have very
short half-lives and deliver a high dose of strongly
ionising alpha particles to a small area of tissue, a
process that can lead to lung cancer.
3.1 The Earth's crust
'Whoever could make two ears of corn grow upon
a spot of ground where only one grew before
would deserve better of mankind than the whole
race of politicians put together.'
Jonathan Swift (1667-1745)
The Earth's crust comprises principally siliceous
rocks, giving it an average elemental composition of:
oxygen, 46.6%; silicon, 27.7%; aluminium, 8.1%;
iron, 5.0%; calcium, 3.6%; sodium, 2.8%; potas-
sium, 2.6%; magnesium, 2.1%. The remaining 75
