Environmental Engineering Reference
In-Depth Information
Beckett et al.
2004
). When concrete, brick, stone, glass, and asphalt surfaces are
heated during the summer period, vertical thermal air movements (upward) are
created and dust particles found on the ground are carried and spread into the air
(Minke and Witter
1982
). Particulate matter is adsorbed by the leaves, trunks, and
twigs (Fig.
6.3
a, b), and is an efficient sink for particulate matter (Fowler et al.
1989
).
According to Hosker and Lindberg (
1982
) fine dust (PM
2.5
and PM
10
) con-
centrations are reduced when particles are adhered to the leaves and stems of
plants. Literature claims that by rainfall the adsorbed particulate matter is washed
off into the soil or substrate below. However, results from a conducted simulated
rainfall experiment (Ottelé
2011
), shows that especially the fine and ultrafine
particles are fixed on the leaf surface. Also falling of leaves in autumn contributes
to particle binding. Research shows for example that plant barriers immediately
along a roadside (daily traffic level 20.000-50.000 vehicles) are more beneficial in
capturing lead (Pb) and cadmium (Cd) particles than plants investigated in the
rural area (Bussotti et al.
1995
).
Also Thönnessen (
2002
) found heavy metal concentrations and fine particles
on leaves of a green façade (Parthenocissus tricuspidata) in the inner city of
Düsseldorf (daily traffic level 12.500 vehicles). Sternberg (
2010
) found the same
results by comparing ivy leaves from different sites (by counting particles on ivy
leaves), the leaves from the sites exposed to a high daily traffic level, had collected
a significant number of particles compared to the sites that are less exposed.
Research at the university of Bonn shows that mosses for example are excellent
fine dust absorbers (Frahm and Sabovljevic
2007
). One square meter of moss can
''consume'' 20 g of fine dust each year. Since moss is one of the easiest plants to
use, for example, on a green roof, is an enormous advantage and cheap method
against (local) air pollution.
Besides particle binding plants are also known to absorb gaseous pollutants
through the stomata (CO
2
and NO
x
). Via photosynthesis CO
2
is sequestered in the
leaves (Minke and Witter
1982
). The negative health effects of particulate matter
pollution for human's stands for decreasing lung functions, increased respiratory
problems, and other health care visits for respiratory and cardiovascular diseases
(Pope et al.
2009
).
Besides these effects also durability problems are involved and include accel-
erated corrosion of metals, as well as damage to paints, sculptures, and soil-
exposed surfaces on man-made structures (United Nations
2007
). The improved
air quality by a green envelope has direct benefits for people who suffer a long
disease. A decrease of smog formation will occur, and also durability or corrosion
problems are reduced of urban infrastructure that is susceptible to damage from air
pollution (United Nations
2007
).
A study carried out by the University of Dresden (Schröder
2009
) with regard to
the organic balance of a greened façade with 1,000 m
2
Hedera helix pointed out
that in one year: 1,019 kg of water and 2,351 kg of CO
2
is consumed and bound,
respectively. In this reaction, 5,854 kg of organic mass (water content 4,409 kg
and dry mass 1,415 kg) and 1,712 kg of O
2
is produced. With the assumption of an
leaf area index (ratio between leaf surface in m
2
and covered wall surface in m
2
)
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