Air Pollution and Global Change 171
They play an important role in the formation of photochemical smog; CH 4
contributes to the greenhouse effect. They come from the exhaust fumes of
cars and from any use or transportation of gasoline, oil and natural gas,
due to the escapes that occur.
Sulphur dioxide (SO 2 ) comes from sulphur contained as an admixture in
solid and fluid fuels. It is formed during combustion and is mainly emitted in
the atmosphere from industries, diesel-driven cars and heating installations.
It has a characteristic odour and contributes to the emergence or aggravation
of respiratory system affections. SO 2 can be oxidized in the atmosphere to
SO 3 which in turn reacts with the vapours and forms sulphuric acid (H 2 SO 4 ).
Ozone (O 3 ) is triatomic oxygen that mainly appears in the stratosphere,
where it forms a characteristic layer (Section 9.3) and absorbs a part of the
incident ultraviolet radiation. It is also found in the troposphere, though,
in a very small concentration that increases by pollution and contributes to
the amplification of the greenhouse effect (Section 9.4); it also has a toxic
action on organisms. It is harmful for plants (80 ppbv reduce the growth
rate) and for human beings (120 ppbv cause respiratory problems, such as
asthma and bronchitis).
Suspended particulate matter (PM) is solids or liquids found in the air.
They are produced by various burnings, by industrial emissions, and by
excavations or other activities that create dust. In the atmosphere of cities,
suspended particulates are to a great extent produced by the exhaust fumes
of cars. Their physical form and chemical composition vary immensely.
Some are big enough or dark enough to be visible as smoke or dust. Others
are so small that they can only be detected by a microscope. Until 1987,
environmental regulations pertained to the total suspended particulate
matter , but now attention is focused on the small or very small particulates
because they are able to reach deeper into the respiratory system and cause
health damage. The EPA limits for PM-10 concentration (particulates with
a diameter up to 10 μm) in the air are 50 μg/m 3 (as a yearly average) and
150 μg/m 3 (as a daily average). They can contain a large variety of substances such as various organic materials, lead, cadmium, mercury, and
asbestos, many of which are toxic or are carcinogens. The PM-10 consequences on health include damages to the respiratory system and to the
lungs, cancer and early death. Elderly people, children and persons suffering from chronic respiratory diseases are more sensitive to suspended
particulate matter. Recent studies show that very small particles (with a
diameter less than 2.5 μm) are even more dangerous, and there is a trend
for the establishment of even lower limits. Suspended particulates are also
emitted by natural and various other sources such as volcanic eruptions,
agricultural and forest production, aeolian erosion and fires. Suspended
particulates can be formed secondarily in the atmosphere through interactions of gaseous pollutants (e.g. SO 2 and NO x ).
They play an important role in the formation of photochemical smog; CH 4
contributes to the greenhouse effect. They come from the exhaust fumes of
cars and from any use or transportation of gasoline, oil and natural gas,
due to the escapes that occur.
Sulphur dioxide (SO 2 ) comes from sulphur contained as an admixture in
solid and fluid fuels. It is formed during combustion and is mainly emitted in
the atmosphere from industries, diesel-driven cars and heating installations.
It has a characteristic odour and contributes to the emergence or aggravation
of respiratory system affections. SO 2 can be oxidized in the atmosphere to
SO 3 which in turn reacts with the vapours and forms sulphuric acid (H 2 SO 4 ).
Ozone (O 3 ) is triatomic oxygen that mainly appears in the stratosphere,
where it forms a characteristic layer (Section 9.3) and absorbs a part of the
incident ultraviolet radiation. It is also found in the troposphere, though,
in a very small concentration that increases by pollution and contributes to
the amplification of the greenhouse effect (Section 9.4); it also has a toxic
action on organisms. It is harmful for plants (80 ppbv reduce the growth
rate) and for human beings (120 ppbv cause respiratory problems, such as
asthma and bronchitis).
Suspended particulate matter (PM) is solids or liquids found in the air.
They are produced by various burnings, by industrial emissions, and by
excavations or other activities that create dust. In the atmosphere of cities,
suspended particulates are to a great extent produced by the exhaust fumes
of cars. Their physical form and chemical composition vary immensely.
Some are big enough or dark enough to be visible as smoke or dust. Others
are so small that they can only be detected by a microscope. Until 1987,
environmental regulations pertained to the total suspended particulate
matter , but now attention is focused on the small or very small particulates
because they are able to reach deeper into the respiratory system and cause
health damage. The EPA limits for PM-10 concentration (particulates with
a diameter up to 10 μm) in the air are 50 μg/m 3 (as a yearly average) and
150 μg/m 3 (as a daily average). They can contain a large variety of substances such as various organic materials, lead, cadmium, mercury, and
asbestos, many of which are toxic or are carcinogens. The PM-10 consequences on health include damages to the respiratory system and to the
lungs, cancer and early death. Elderly people, children and persons suffering from chronic respiratory diseases are more sensitive to suspended
particulate matter. Recent studies show that very small particles (with a
diameter less than 2.5 μm) are even more dangerous, and there is a trend
for the establishment of even lower limits. Suspended particulates are also
emitted by natural and various other sources such as volcanic eruptions,
agricultural and forest production, aeolian erosion and fires. Suspended
particulates can be formed secondarily in the atmosphere through interactions of gaseous pollutants (e.g. SO 2 and NO x ).