Environmental Engineering Reference
In-Depth Information
in the indicated roads from 92 to 78 km h
−1
, that is, a difference of 14 km h
−1
. On
the contrary, the intensity of traffic has been similar for both years analysed
(47,859 daily average traffic -DAT- during January-August 2007 and 47,606
DAT in the period January-August 2008). For September-November there is a
decrease in DAT of 5.9% (49,795 vs. 46,883 DAT for the years 2007 and 2008,
respectively). Therefore it should be highlighted that the differences in emissions
and air quality are caused by the limitation of the speed and not because of
modifications in the intensity of traffic. However, several monthly differences in
the DAT are depicted (both increases and decreases) caused by the temporal
variation of holidays (Eastern, summer holidays, etc.) and their corresponding
special traffic patterns. The limitation of the speed together with the reduction in
the congestion lead to a diminution in the fuel consumption. The fuel consumption
is reduced in 40.8 t day
−1
for gasoline and 46.6 t day
−1
for diesel; that is, an annual
reduction of 4% in the Barcelona Metropolitan Area (over 30,000 t of fuel/year).
Since the CO
2
emissions are directly proportional to the fuel consumption, the
reduction in the emission of this greenhouse gas is also around 4% (over 94,000
t/year). The variation in the fuel consumption leads to a reduction in the emissions
of primary pollutants in the whole metropolitan area around 4% for NO
x
, PM2.5,
PM10, SO
2
and CO. As an example, for the nitrogen oxides, the emissions
diminish in 1.85 t day
−1
(4.36%). For the particulate matter (PM10) emissions are
reduced in 0.13 t day
−1
(3.95%). The main reductions of emissions are achieved
over the access roads to the city of Barcelona. If we consider just the areas with
control of the circulation speed to 80 km h
−1
, the fuel consumption reduces about
10.4%. This also affects the emissions, which are reduced in a 14.81% for CO,
10.98% for nitrogen oxides, 12.47% for PM2.5 and 10.99% for PM10.
Regarding air quality implications, the speed limitation involves a reduction in
ground levels of atmospheric pollutants in the whole area where the measure is
implemented. Specifically, the improvement of air quality is especially effective in
the areas close to the access roads. In this sense, several domains have been
defined according to the name of the road where they have been implemented:
inside the Barcelona city ring roads (IRR), A2-C32, AP2, C31 and C32 (
Fig. 2)
.
The measure takes importance in the domains A2-C32, AP2, C31 and C32 where
the levels of NO
x
are reduced 5-8% on average. For the particulate matter the
reduction is around 3%, with reductions for several days over 10-15%. Improve-
ments for sulphur dioxide are lower (around 1%). The NO
x
emissions decrease in
a VOCs limited area, such as the Barcelona city, and it produces local increases of
O
3
concentrations, especially in the urban plume over the roads affected by the
speed limit (up to 1-2%); nevertheless the O
3
concentrations in downwind areas
remain practically constant. It is also noticeably how air quality is also improved
in areas far from those roads where the speed limitation has not come into effect
(IRR); here the air quality improvements are around 1%.
