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Introduction
Objective
of the study, carried out by the Provincial Department of the Veneto Regional
Environmental Protection Agency (ARPAV) and commissioned by
the City of Venice, is the characterization of the contribution to CO, C6H6 and PM10
levels in the urban area of Mestre, caused by the
presence of its Circular Road.
The Circular
Road of Mestre
is a trunk road that links the Turin-Mestre section
of the A4 Highway (Venezia-Villabona tollbooth) to the Mestre-Trieste
section of the same Highway (at the junction with the Mestre-Belluno
A27 Highway and the ring road to the Tessera Airport, see blue map).
It is 10 km long, but is one of Italy’s busiest
highway sections. It is crossed daily by about 175.000 vehicles, and
about 64 millions vehicles per year. All these vehicles, a large share of which are heavy duty vehicles (belonging
also to Eastern European countries), cross the Circular Road both to reach Mestre, or to go, for example, from Trieste to Turin, or
from Rome to Northern Italy. The passage of all these vehicles puts serious
pressure on the atmospheric environment of Mestre.
Evaluation tools
The dispersion model used for the evaluation of the
atmospheric pollution caused by the Circular
Road, is ADMS-Urban, recommended to study the dispersion of
the pollutants emitted by linear-type sources (roads).
Through the application of this model it has been
possible to characterize the spatial distribution of CO, C6H6
and PM10 levels.
Each receptor has been represented by the average value in time and also by the
worst case, that is the maximum time polluting
concentration obtained during the considered period. The temporal and traffic scenario refers to
2002, therefore preceding the structural modifications to the Circular
Road which now consists of three lanes
in both directions and which was obtained by using the two emergency lanes.
Input data
The input data used for running the dispersion model
is as follows:
Traffic flows and speed: this
comes from the Padova-Venezia S.p.A.
Highway Company (that manages part of the Circular Road) and is experimentally
surveyed every 5 minutes within a 24 hour period and includes a distinction
between light (length ≤ 5.5 m) and heavy duty vehicles (length > 5.5
m) and winter and summer. This data has
been compared with that relating to the rush hour only (7.30 – 8.30) and shared
between light and heavy vehicles which is what was
given by the Municipality of Venice
Mobility Office as output of the EMME2
traffic model.
Emission data: calculated following the
European COPERT III methodology.
Meteorological data: surveyed from the
Industrial Area Authority of Porto Marghera
monitoring network (wind speed, prevalent wind direction, air temperature as
measured by the station at 10 meters in height, global or incidental solar
radiation as read by the station at 4 meters in height) and from the Synoptic
station of the Marco Polo airport (cloudiness derived from the tri-hour Synop data, spatially and temporally interpolated with
those of the neighbouring meteorological stations belonging to the ARPAV
Network at the Meteorological Centre of Teolo).
Geometrical data: the Circular
Road has been divided into 57 links,
including the access ramps and the junctions.
Output
data
For carbon
monoxide (CO) it has been observed that:
·
the highest concentration (5.9 mg/m3) is associated with Saturday rush hour
(17-18), in winter time;
·
the simulated
concentration does not ever reach the limit value of 10 mg/m3 (taken
as the quantitative reference term).
For
benzene (C6H6) it has been observed that:
·
the highest concentration
(62 μg/m3) is
associated with Saturday rush hour (17-18), in winter time;
·
the
percentage of receptors whose simulated concentration exceeds the annual limit
value of 10 μg/m3
(taken as quantitative reference term) is very high. In this case it is
important to remember that what is reported, for each position in space, is the
maximum value reached in the examined period;
·
the average
concentrations of the winter and summer semester have a simulated maximum value
of 9 and 5 μg/m3
respectively. Both values are below that assumed as reference (10 μg/m3).
For PM10 it has been observed
that:
·
the highest concentration
(112 μg/m3) is
associated with weekday’ rush hour (8-9), in winter time;
·
the
percentage of receptors whose simulated time concentration exceeds the daily
limit value of 65 μg/m3, not to be exceeded more than 35 times
per year (starting from 01.01.2002, taken as quantitative reference term) does
not exceed 25% of cases. Also in this case it has to be remembered that what is
reported, for each position in the space, is the maximum value reached in the
examined period;
·
the average
concentrations of the winter and summer semester have a simulated maximum value
of 17 and 10 μg/m3,
respectively. Both values are below the annual limit value of
44.8 μg/m3,
which came into force from the 01.01.2002.
Conclusions
With reference to the rush hour, the Circular Road contributes to 17% of the total CO emissions, to 17% of the
C6H6 emissions and to 26% of PM10 in
comparison to the emission produced by the entire urban area of Mestre. If we add other main urban roads neighbouring the
urban area (5 links of considerable length) to the Circular
Road, the percentage contribution to total emissions during
the rush hour in the extra-urban sector reaches 31% for CO, 30% for C6H6 and 46% for PM10.
For CO and C6H6,
the concentration estimated by the model represents the contribution of the Circular
Road to the overall pollution in a
determined position (so called receptor) that, actually, adds to the pollution
produced by the neighbouring urban roads.
Also for PM10
only the primary contribution has been calculated because it is not
possible to evaluate, through the available information, the secondary one
(associated to complex chemical reactions that take place in the atmosphere and
involve various pollutants, giving birth to further shares of PM10
pollution, not directly emitted from polluting sources) and the re-suspension of ground PM10
(the most recent scientific acquisitions say that such contribution is
relevant, but a reference methodology to quantify them is not yet available).
Certainly, even if not exactly evaluated, the secondary and re-suspension contributions to the overall PM10 concentration,
measurable at a given position in the space, is extremely relevant; the
evidence is that the historical series and the annual averages for PM10
measured by different monitoring stations of air quality (background station,
urban hot spot station, etc.), belonging to the ARPAV Network present in the
urban area of Mestre, are perfectly matched.
The annual averages updated to December 2002 are
respectively 45 μg/m3
for the urban hot spot station, 47 μg/m3 for the urban background one
and 45 μg/m3 for the
residential area. The monitoring data portray a particularly difficult
situation for 2002: the annual reference value (44.8 μg/m3)
has in fact been exceeded in all the stations and the daily reference value for
2002 of 65 μg/m3,
not to be exceeded more than 35 times per year, has actually been exceeded
circa 78 times in at least one of the three mentioned monitoring stations. |
