406
E. M. Koriesh and I. H. Abo-Soud
of open space separating or interrupting urban development. A land so designated
is controlled through regulation or public or quasi-public ownership (such as the
Nature Conservancy) to retain its natural character and provide a resemblance of
rural ambience in urban or urbanizing areas [172].
The central goal of Roosevelt’s greenbelt programme, an innovative and radical
intervention in American city building, was not to create better urban communities,
but rather to generate jobs in a declining national economy.
18.2 Air Pollutant Uptake by Vegetation
Vegetation acts as CO 2 sink, and some species can utilize air pollutants effectively.
Plants also intercept tones of dust and serve as acoustic screens on busy highways and
noisy factory areas. Several plants can collect the dust suspended in the atmosphere
and dilute the concentration of toxic and harmful gases like SO 2 , CO 2 , etc. Trees
have been reported to remove air pollutants like hydrogen fluoride, SO 2 , and some
compounds of photochemical reactions and collect heavy metals like mercury (Hg)
and lead (Pb) from the air [174, 175].
After absorbing the air pollutants, trees change them to harmless metabolites
through various physiological processes. Of course, every plant can not be an agent
of air pollution control; only those which can tolerate pollutants can act as attenuators [176]. All-in-all, increasing vegetation in the cities, towns, and industrial
establishments holds great potential to combat air pollution.
Plants remove pollutants from the air in three ways, viz.
1. Absorption by the leaves,
2. Deposition of particulate and aerosols on leaf surface, and
3. Fallout of particulate on the leeward (downwind) side of the vegetation because
of the slowing of the air movement [177, 101].
18.3 Removal of Gaseous Pollutants
Amble evidence is available to support the view that plants in general and trees in
particular function as sinks for gaseous pollutants (and other pollutants by roots,
phytoremediation). The latter are transferred from the atmosphere to vegetation by
the combined forces of diffusion and flowing air movement. Once in contact with
plants, gases may be bound or dissolved on exterior surfaces or be taken up by the
plants via stomata. If the surface of the plant is wet and if the gas is water soluble,
the former process can be very important.
When the plant is dry or in the case of gases with relatively low water solubility,
the mechanism is assumed to be the most important [178]. Plant uptake rates increase
E. M. Koriesh and I. H. Abo-Soud
of open space separating or interrupting urban development. A land so designated
is controlled through regulation or public or quasi-public ownership (such as the
Nature Conservancy) to retain its natural character and provide a resemblance of
rural ambience in urban or urbanizing areas [172].
The central goal of Roosevelt’s greenbelt programme, an innovative and radical
intervention in American city building, was not to create better urban communities,
but rather to generate jobs in a declining national economy.
18.2 Air Pollutant Uptake by Vegetation
Vegetation acts as CO 2 sink, and some species can utilize air pollutants effectively.
Plants also intercept tones of dust and serve as acoustic screens on busy highways and
noisy factory areas. Several plants can collect the dust suspended in the atmosphere
and dilute the concentration of toxic and harmful gases like SO 2 , CO 2 , etc. Trees
have been reported to remove air pollutants like hydrogen fluoride, SO 2 , and some
compounds of photochemical reactions and collect heavy metals like mercury (Hg)
and lead (Pb) from the air [174, 175].
After absorbing the air pollutants, trees change them to harmless metabolites
through various physiological processes. Of course, every plant can not be an agent
of air pollution control; only those which can tolerate pollutants can act as attenuators [176]. All-in-all, increasing vegetation in the cities, towns, and industrial
establishments holds great potential to combat air pollution.
Plants remove pollutants from the air in three ways, viz.
1. Absorption by the leaves,
2. Deposition of particulate and aerosols on leaf surface, and
3. Fallout of particulate on the leeward (downwind) side of the vegetation because
of the slowing of the air movement [177, 101].
18.3 Removal of Gaseous Pollutants
Amble evidence is available to support the view that plants in general and trees in
particular function as sinks for gaseous pollutants (and other pollutants by roots,
phytoremediation). The latter are transferred from the atmosphere to vegetation by
the combined forces of diffusion and flowing air movement. Once in contact with
plants, gases may be bound or dissolved on exterior surfaces or be taken up by the
plants via stomata. If the surface of the plant is wet and if the gas is water soluble,
the former process can be very important.
When the plant is dry or in the case of gases with relatively low water solubility,
the mechanism is assumed to be the most important [178]. Plant uptake rates increase