Chapter 9
Air Pollution – Particulate Matter
9.1 INTRODUCTION
Particulate air pollution refers to the presence of small solid and liquid aerosols
suspended in the atmosphere. The physical dimensions and chemical properties
of these aerosols vary greatly. Their sizes may vary from 0.5 mm to 10
À7 mm,
and they are composed of a large number of inorganic and organic materials,
including metals and nonmetal elements (and their oxides, nitrates, and
sulfates). Although it is often convenient to group them as particulates, their
sources, distribution, and effects can be highly variable. Because of the large
quantities of particulates emitted into the atmosphere and the potential adverse
effects they elicit, the U.S. Environmental Protection Agency (EPA) has
designated particulate matter (PM) as one of the six ‘‘Criteria Air Pollutants’’
to be regulated. In 1987, the agency added a new standard for particulates,
called PM 10 (referring to PM with a diameter less than 10 mm), based on the
evidence that the smaller PM has the greatest impact on health because of its
capacity to be inhaled. This chapter presents an overview of this class of air
pollutants, followed by discussion of three specific examples of PM: silica,
beryllium, and asbestos.
9.2 CHARACTERISTICS
Particulates are usually classified into primary or secondary. Primary
particulates are larger (usually 1 to 20 mm in diameter) and are emitted
directly into the atmosphere by a variety of chemical and physical processes.
Secondary particulates are relatively smaller and are formed by chemical
reactions occurring in the atmosphere.
1 The composition of particulates varies
from place to place, and includes thousands of entities that differ in size,
surfaces, and toxicity.
2 Particles in most urban aerosols have been shown to
contain a number of potentially toxic trace species, such as lead (Pb), cadmium
(Cd), nickel (Ni), selenium (Se), vanadium (V), zinc (Zn), bromine (Br), cobalt
(Co), manganese (Mn), sulfate, and benzo[a]pyrene.
3
Evidence from recent studies strongly suggests the importance of the
primary urban aerosols. It is considered that even though these primary
aerosols contribute a minor amount to the total mass of aerosols, they serve as
condensation nuclei upon which the secondary aerosol mass resides and they
carry the bulk of the particulate toxins.
4
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135
Air Pollution – Particulate Matter
9.1 INTRODUCTION
Particulate air pollution refers to the presence of small solid and liquid aerosols
suspended in the atmosphere. The physical dimensions and chemical properties
of these aerosols vary greatly. Their sizes may vary from 0.5 mm to 10
À7 mm,
and they are composed of a large number of inorganic and organic materials,
including metals and nonmetal elements (and their oxides, nitrates, and
sulfates). Although it is often convenient to group them as particulates, their
sources, distribution, and effects can be highly variable. Because of the large
quantities of particulates emitted into the atmosphere and the potential adverse
effects they elicit, the U.S. Environmental Protection Agency (EPA) has
designated particulate matter (PM) as one of the six ‘‘Criteria Air Pollutants’’
to be regulated. In 1987, the agency added a new standard for particulates,
called PM 10 (referring to PM with a diameter less than 10 mm), based on the
evidence that the smaller PM has the greatest impact on health because of its
capacity to be inhaled. This chapter presents an overview of this class of air
pollutants, followed by discussion of three specific examples of PM: silica,
beryllium, and asbestos.
9.2 CHARACTERISTICS
Particulates are usually classified into primary or secondary. Primary
particulates are larger (usually 1 to 20 mm in diameter) and are emitted
directly into the atmosphere by a variety of chemical and physical processes.
Secondary particulates are relatively smaller and are formed by chemical
reactions occurring in the atmosphere.
1 The composition of particulates varies
from place to place, and includes thousands of entities that differ in size,
surfaces, and toxicity.
2 Particles in most urban aerosols have been shown to
contain a number of potentially toxic trace species, such as lead (Pb), cadmium
(Cd), nickel (Ni), selenium (Se), vanadium (V), zinc (Zn), bromine (Br), cobalt
(Co), manganese (Mn), sulfate, and benzo[a]pyrene.
3
Evidence from recent studies strongly suggests the importance of the
primary urban aerosols. It is considered that even though these primary
aerosols contribute a minor amount to the total mass of aerosols, they serve as
condensation nuclei upon which the secondary aerosol mass resides and they
carry the bulk of the particulate toxins.
4
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-009.3d]
Ref: 4365 MING-HO YU Chap-009 Page: 135 135-148
135