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E. M. Koriesh and I. H. Abo-Soud
9.2 Removal of Particulate Pollutants
Suspended particles in the atmosphere are deposited on plant surfaces by three
processes:
1. sedimentation under the influence of gravity,
2. impaction under the influence of eddy currents, and
3. deposition under the influence of precipitation.
Sedimentation regularly results in the deposition of particles on the different
aboveground plant parts and increases onupper surface of leaves and is most important with large particles. Sedimentation velocity varies with particle mass, size [97],
particle density, nutrient and organic matter content [98], shape, and trace elements
[99] and other factors. Impaction happen when air flows fast on the obstacle, and the
air stream divides, but particles in the air be likely to continue in a straight track due
to their momentum and strike the obstacle.
The efficiency of the collection via impaction is the principal means of deposition
if:
(a) particle size is of the order of tens of micrometers or greater,
(b) obstacle size is of the order of centimeters,
(c) approach velocity is of the order of meters per second or more, and
(d) the collecting surface is wet, sticky, hairy or otherwise retentive.
Ingold [100] presented data indicating that leaf petioles are considerably more
efficient particulate impactors than either twigs (stems) or leaf lamina. For particles
of dimension 1–5 μm, impaction is not efficient, and interception by fine hairs on
vegetation is possibly the most efficient retentive mechanism [101].
The transfer of particles from the atmosphere to natural surfaces is commonly
expressed via deposition velocity. For small particles, for example, condensation
aerosols less than 1 μm, deposition velocities are much less than for large particles:
For example, spores and pollen 20–40 μm in diameter.
Trace metals, especially heavy metals, are most commonly associated with fine
particles in contaminated atmospheres.
Trace element investigations conducted in roadside, industrial, and urban environments have dramatically demonstrated the impressive burdens of particulate heavy
metals that can accumulate on vegetative surfaces.
Based on a literature survey, particulate removal efficiencies for trees have been
estimated (Table 2). It is based on the following assumptions:
Particulate average deposition velocity of 1 cm s
−1 for trees and 0.8 cm s
−1 for
grass and weeds, leaf area index of 5.1 for deciduous trees and 2.3 for conifers, and
approximately 2 ha of deciduous tree surface and 1 ha of coniferous tree surface ha
−1
of land area.
Black carbon and particulate matter are not a gas, but it acts as a greenhouse gas.
It can be hanging in the air and absorb heat [102]. Gardeners may cause more carbon
particulates in the atmosphere by burning garden wastes.
E. M. Koriesh and I. H. Abo-Soud
9.2 Removal of Particulate Pollutants
Suspended particles in the atmosphere are deposited on plant surfaces by three
processes:
1. sedimentation under the influence of gravity,
2. impaction under the influence of eddy currents, and
3. deposition under the influence of precipitation.
Sedimentation regularly results in the deposition of particles on the different
aboveground plant parts and increases onupper surface of leaves and is most important with large particles. Sedimentation velocity varies with particle mass, size [97],
particle density, nutrient and organic matter content [98], shape, and trace elements
[99] and other factors. Impaction happen when air flows fast on the obstacle, and the
air stream divides, but particles in the air be likely to continue in a straight track due
to their momentum and strike the obstacle.
The efficiency of the collection via impaction is the principal means of deposition
if:
(a) particle size is of the order of tens of micrometers or greater,
(b) obstacle size is of the order of centimeters,
(c) approach velocity is of the order of meters per second or more, and
(d) the collecting surface is wet, sticky, hairy or otherwise retentive.
Ingold [100] presented data indicating that leaf petioles are considerably more
efficient particulate impactors than either twigs (stems) or leaf lamina. For particles
of dimension 1–5 μm, impaction is not efficient, and interception by fine hairs on
vegetation is possibly the most efficient retentive mechanism [101].
The transfer of particles from the atmosphere to natural surfaces is commonly
expressed via deposition velocity. For small particles, for example, condensation
aerosols less than 1 μm, deposition velocities are much less than for large particles:
For example, spores and pollen 20–40 μm in diameter.
Trace metals, especially heavy metals, are most commonly associated with fine
particles in contaminated atmospheres.
Trace element investigations conducted in roadside, industrial, and urban environments have dramatically demonstrated the impressive burdens of particulate heavy
metals that can accumulate on vegetative surfaces.
Based on a literature survey, particulate removal efficiencies for trees have been
estimated (Table 2). It is based on the following assumptions:
Particulate average deposition velocity of 1 cm s
−1 for trees and 0.8 cm s
−1 for
grass and weeds, leaf area index of 5.1 for deciduous trees and 2.3 for conifers, and
approximately 2 ha of deciduous tree surface and 1 ha of coniferous tree surface ha
−1
of land area.
Black carbon and particulate matter are not a gas, but it acts as a greenhouse gas.
It can be hanging in the air and absorb heat [102]. Gardeners may cause more carbon
particulates in the atmosphere by burning garden wastes.