9.3 FORMATION OF PARTICULATES
Particulates are formed from both natural and anthropogenic sources. Natural
sources include volcanic ash, wildfire particles, fine soil particles, fine marine
salts from ocean spray, biological particles such as pollen, fungal spores, etc.
Fine particulates are also produced by atmospheric reactions among gases,
such as through photochemical reactions. Anthropogenic sources include a
variety of industrial combustion processes, mining, vehicle emissions, domestic
heating and cooking, pottery making, metalworking, and many other
manufacturing processes. In addition, cultivation of agricultural land also
contributes significant amounts of PM, through land clearance and fire control
activities.
9.3.1 PHYSICAL PROCESSES
Particulate matter can be formed through both physical and chemical
processes. Particles above approximately 1 mm in size are generally formed
by the disintegration of larger particles. This is called a dispersion process, and
the product is known as a dispersion aerosol. Dusts are solid dispersion
aerosols, which may be formed through a variety of natural and human
activities. Some examples include: volcanic eruption, wind-blown dust from
dry soil, ocean spray, coal grinding, rock crushing, stone cutting and polishing,
high-power drilling of tunnel rocks, and manufacture of pottery.
9.3.2 CHEMICAL PROCESSES
Both inorganic and organic particles are produced through various chemical
processes. Metal oxides form a major class of inorganic particles in the
atmosphere. They are produced whenever fuels containing metals are burned.
For instance, particulate iron oxide is produced in the combustion of coal that
contains iron sulfide (FeS 2 ) as a contaminant:
3FeS 2 þ 8O 2 ! Fe 3 O 4 þ 6SO 2
ð9:1Þ
As noted in Section 8.2, sulfuric acid (H 2 SO 4 ) mists are formed from the
oxidation of atmospheric sulfur dioxide (SO 2 ):
2SO 2 þ O 2 þ 2H 2 O ! 2H 2 SO 4 (liquid droplets)
ð9:2Þ
The sulfuric acid thus formed can react with basic air pollutants, such as
ammonia (NH 3 ), calcium oxide (CaO), lead oxide (PbO), or aluminum oxide
(Al 2 O 3 ), forming various sulfates:
H 2 SO 4 ðdropletÞ þ 2NH 3 ðgasÞ ! ðNH 4 Þ 2 SO 4 ðdropletÞ
ð 9:3Þ
H 2 SO 4 ðdropletÞ þ PbOðparticleÞ ! PbSO 4 ðdropletÞ þ H 2 O
ð9:4Þ
136
Environmental Toxicology
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-009.3d]
Ref: 4365 MING-HO YU Chap-009 Page: 136 135-148
Particulates are formed from both natural and anthropogenic sources. Natural
sources include volcanic ash, wildfire particles, fine soil particles, fine marine
salts from ocean spray, biological particles such as pollen, fungal spores, etc.
Fine particulates are also produced by atmospheric reactions among gases,
such as through photochemical reactions. Anthropogenic sources include a
variety of industrial combustion processes, mining, vehicle emissions, domestic
heating and cooking, pottery making, metalworking, and many other
manufacturing processes. In addition, cultivation of agricultural land also
contributes significant amounts of PM, through land clearance and fire control
activities.
9.3.1 PHYSICAL PROCESSES
Particulate matter can be formed through both physical and chemical
processes. Particles above approximately 1 mm in size are generally formed
by the disintegration of larger particles. This is called a dispersion process, and
the product is known as a dispersion aerosol. Dusts are solid dispersion
aerosols, which may be formed through a variety of natural and human
activities. Some examples include: volcanic eruption, wind-blown dust from
dry soil, ocean spray, coal grinding, rock crushing, stone cutting and polishing,
high-power drilling of tunnel rocks, and manufacture of pottery.
9.3.2 CHEMICAL PROCESSES
Both inorganic and organic particles are produced through various chemical
processes. Metal oxides form a major class of inorganic particles in the
atmosphere. They are produced whenever fuels containing metals are burned.
For instance, particulate iron oxide is produced in the combustion of coal that
contains iron sulfide (FeS 2 ) as a contaminant:
3FeS 2 þ 8O 2 ! Fe 3 O 4 þ 6SO 2
ð9:1Þ
As noted in Section 8.2, sulfuric acid (H 2 SO 4 ) mists are formed from the
oxidation of atmospheric sulfur dioxide (SO 2 ):
2SO 2 þ O 2 þ 2H 2 O ! 2H 2 SO 4 (liquid droplets)
ð9:2Þ
The sulfuric acid thus formed can react with basic air pollutants, such as
ammonia (NH 3 ), calcium oxide (CaO), lead oxide (PbO), or aluminum oxide
(Al 2 O 3 ), forming various sulfates:
H 2 SO 4 ðdropletÞ þ 2NH 3 ðgasÞ ! ðNH 4 Þ 2 SO 4 ðdropletÞ
ð 9:3Þ
H 2 SO 4 ðdropletÞ þ PbOðparticleÞ ! PbSO 4 ðdropletÞ þ H 2 O
ð9:4Þ
136
Environmental Toxicology
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-009.3d]
Ref: 4365 MING-HO YU Chap-009 Page: 136 135-148