Chemistry Reference
In-Depth Information
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Contribution of resuspension to total modelled pm10
Contribution of road transport to dust concentration
Fig. 5 LOTOS-EUROS relative contributions from traffic-induced resuspension to modelled dust
(
left
) and PM
10
(
right
) concentrations
probably the most difficult source to track given the few existing emission tests
[
152
] and the chemical similarity to other mineral sources (construction materials,
soil, etc.). Cu and Sb ambient concentrations and their ratio have already been
shown in the literature to be useful chemical tracers for brake wear-related
emissions. Brake wear emissions may be responsible for 50-75% of the total copper
emissions to air for most of Western Europe [
153
]. Brake pad compositions
normally show values for Cu/Sb in the range of 9-18 [
154
,
155
] although it can
be below 2 [
156
] depending on the manufacturer. When referring to ambient
concentrations of Cu and Sb in the PM
10
fraction the ratio Cu/Sb lies between 4
[
157
] to more common values of 7-9 in most urban sites [
2
,
32
,
121
,
158
-
162
]). In
road dust samples [
109
] found a rather constant Cu/Sb ratio (6.8
0.9) only at one
city (Barcelona), while in Z¨rich and Girona, the ratio was varying considerably,
being the average values 13.5
8.9, respectively.
Contribution estimates of wear emissions in Europe are still few [
30
,
32
,
134
,
163
,
164
]. The few estimates over Europe were found to vary from negligible up to
4.0
6.1 and 17.0
g/m
3
(10% of daily measured PM
10
mass. At a regional scale, brake wear
emissions contribute up to 2
m
g/m
3
(Fig.
6
). Although the contribution of brake
particles is not dominant in terms of mass, their health concern might be the most
relevant. After the ban of asbestos fibres for brakes manufacturing in the mid-1990s,
composition of brake linings has rapidly changed, but there is still a number of
possible toxics used and the information on materials employed by each manufac-
turer is missing. Generally, materials used for brake linings include metallic friction
materials (Fe and Fe-Cu oxides), lubricants (graphite and Fe-Sb-Mo-Sn-Mn
sulphides) and mineral fibres (Barite, Calcite, Zircon and Al-silicates) used as fillers.
However, the composition can change largely from one brand to another and from
one country to another. Also, the composition and size of brake particles can change
during braking due to the high temperature and friction stress. As an example, at
m
