Environmental Engineering Reference
In-Depth Information
Table 1
Internal and external UFP concentrations
Ratio -
external/
internal
Internal PNC (#/cm
−3
)
External PNC (#/cm
−3
)
Description
Session
Mean
Max
SD
Mean
Max
SD
Entire Route
Peak
14,108
41,624
5,650
85,711
397,604
94,366
6.1
Non-tunnel only
Peak
14,130
41,624
5,738
62,664
391,874
65,616
4.4
East bore
Peak
10,931
19,987
2,843
304,731
397,604
64,715
27.9
West bore
Peak
11,434
28,874
2,366
257,625
388,860
68,885
22.5
Entire route
Inter-peak
14,036
47,627
4,954
73,539
394,952
79,755
5.2
Non-tunnel only
Inter-peak
13,933
47,627
4,855
55,102
383,408
54,857
4.0
East bore
Inter-peak
17,302
17,777
4,319
262,221
394,952
61,043
15.2
West bore
Inter-peak
15,205
30,996
4,997
212,507
318,803
52,152
14.0
304,731 particles cm
−3
, whereas
[9]
found that measurements within the Grande
Mare tunnel were higher during the afternoon period, averaging in excess of
400,000 particles cm
−3
. This difference is likely to relate to the different lengths of
the two tunnels, different diurnal profiles and fleet composition. To put these values
into perspective,
[23]
sampled PNCs within residential flats near a busy road and
measured indoor concentrations of approximately 10,000 particles cm
−3
. Assuming
this observation is typical of indoor environments, particle concentrations within the
Westgate tunnel are therefore up to 30 magnitudes greater than an indoor environment,
where sources of particles are controlled and limited to infiltration through the
infrastructure of the building.
Spatial variation in external concentrations:
Averaged external PNC profiles
along the route for the peak and inter-peak periods are presented in Figs.
4
and
5
.
Although similar shaped profiles can be seen for the two sampling periods, concen-
trations are higher within both tunnel bores during the peak period. Steep increases
are seen prior to entering both tunnel bores, starting on average 124 m from the
tunnel entrances, with the greatest relative increase seen at the westbound tunnel
where concentrations rise by a factor of 3.43 and 5.35 for peak and inter-peak peri-
ods respectively, representing an increase of 1,361 and 1,892 particles cm
−3
m
−1
travelled for these periods. For the eastbound bore, concentrations increase by a
factor of 2.35 and 2.60 for the two periods - representing an average increase of 1,264
particles cm
−3
m
−1
travelled. Away from the tunnel, other PNC events are evident in
both peak and inter-peak periods at similar distances (and therefore geographical
locations) along the route.
Internal concentrations:
Figure
4
shows the variation in internal exposure levels
for both the peak and inter-peak periods (plotted on secondary axis). Averaged over
the entire route, internal concentrations are 6.1 and 5.2 magnitudes less than the
corresponding external concentrations for the peak and non-peak period respectively
(Table
1
). This shows that keeping windows closed and recirculating air in the vehicle
period considerably reduce in-cabin exposure of particles along the entire route.
Within the tunnel microenvironment, during the peak period internal concentrations
are up to 22 to 27 magnitudes less than external levels. This ratio is less during the
non-peak period (14-15.2 for West and East bores respectively).
