Chemistry Reference
In-Depth Information
and emission potentials returned to their pre-sanding levels within 8 h of the sand
application [
131
]. Hussein et al. [
132
] stated that as compared to friction tyres,
studded tyres may increase the road dust resuspension by a factor of 2.0-6.4.
Kantamaneni et al. [
133
] found that the addition of traction material increased
emission factor from 1.04 to 1.45 g veh
1
km
1
. Moreover, when roads were
sanded, the correlation found between emission factors and relative humidity was
not observed. Concerning road dust contributions Swietlicki et al. [
59
] estimated
that road dust source was explaining 32% and 54% of the variance of PM
10
and PM
coarse levels in the city of Lund (Sweden) during Spring. In Copenhagen W˚hlin
et al. [
134
] estimated by means of COPREM receptor modelling that road dust
resuspension accounted for 8
gm
3
of the kerbside PM
10
mass, while motor
m
gm
3
. Such difference was even greater for particles in the
coarse size fraction. In a number of studies from Scandinavia, vehicle exhaust
emissions have been found to contribute only around 10% to traffic-related PM
10
emissions, with much of the remainder accountable for by resuspension [
135
,
136
].
The emission factors (EF) for road dust emissions, expressed in mg per vehicle
per km trabelled (mg v kt
1
), can be inferred from road dust loadings values
(mg m
2
) by means of empirical formulas available in literature [
137
-
140
]. Beside
these methods, there are several experimental approaches followed to estimate road
dust EFs. Most used are the so-called upwind-downwind approach [
141
], the linear
relation between NO
x
and PM
10
[
142
,
143
] and the use of SF6 as tracer [
144
].
The number of studies estimating road dust emission factors is, however, still very
limited and observational studies are rather incomplete. In other words, the
emission estimates do not fully represent the wide range of conditions that are
present within Europe. Emissions vary depending not only on climatic and
meteorological conditions (impact of droughts, road moisture, precipitation, etc.)
but also on road type (residential, motorway, congested road, etc.), vehicle type
(passenger cars, light duty and heavy duty vehicles) and pavement type. In urban
paved roads a negative correlation between road humidity and dust emission factors
was found by Kantamaneni et al. [
133
]. Based on the limited literature available,
regional differences can be observed, with values ranging from 14-23 mg v kt
1
(UK) to 17-92 mg v kt
1
(Switzerland, only LDV), 57-109 mg v kt
1
and
46-108 mg v kt
1
for Germany and Denmark, respectively, 85 mg v kt
1
in
Spain, 121 mg v kt
1
in Finland and 198 mg v kt
1
in Sweden [
140
,
145
-
147
].
On freeways, based on the limited literature available, the reported emission factors
lower, ranging within 10-47 mg v kt
1
[
130
,
146
,
148
,
149
].
Once the emission factors and their variability are estimated, dispersion models
can be used in order to enable point data to be interpreted in terms of geographical
distribution of source contributions, as suggested by the Air Quality Directive
(2008/50/EC). This could serve as a basis for calculating the collective exposure
of the population living in the area and for assessing air quality with respect to the
limit values. Dispersion models are based on the use of meteorological data,
modules to account with physico-chemical processes occurring in the atmosphere
and EFs.
exhausts reached 6
m
