Chemistry Reference
In-Depth Information
grain size and their potential cardiovascular and cerebrovascular adverse health
effects [
103
].
The current and upcoming EURO regulations are expected to achieve major
reductions in ambient concentrations of BC in urban environments and thus, BC is
expected to not pose relevant health and air quality problems in the coming future.
However, the implementation of technological solutions such as particle filter traps
or stripping of exhaust gases has resulted in increased emissions in terms of NO
2
,
especially primary NO
2
. Therefore, the relationships between traffic-related
pollutants (e.g., NO
2
/BC, NO
2
/CO ratios) are also changing as a function of these
mitigation strategies.
3 Non-exhaust Emissions
The complexity of the urban environment does not always allow for a clear
separation of road traffic sources; consequently, most of source apportionment
studies present results only for total contributions from road traffic. It is also
common to find studies where the road dust component of traffic emissions is
mixed with other mineral/soil sources. Nevertheless, for air quality management
and exposure studies it is important to understand the individual source
contributions. PM contributions from vehicular traffic should be differentiated
between exhaust and non-exhaust. Ideally non-exhaust contributions should be
further separated between road dust, brake, tyre and road wear.
Differentiating the contribution of road dust from the exhaust is problematic but
a key task since different processes are involved and different control measures/
strategies are necessary. The relative importance of these two categories changes
widely in space and in time. Spatially, road dust emissions increase largely not only
in Southern Europe (due to drier climate) and Scandinavian countries (due to road
sanding and the use of studded tyres) but also within a city environment, e.g. next to
construction sites and in heavy traffic roads. Timely, road dust emissions are
severely influenced by meteorology (precipitation, insulation, road humidity and
droughts). In addition, it is important to monitor the relative increase of non-exhaust
emissions (currently uncontrolled) against the motor exhaust emissions, which have
been progressively reduced in the last two decades by means of the EUROx
legislation. Due to their relatively coarser size distribution (typically between 1
and 10
m) non-exhaust emissions contribute significantly in terms of mass to the
atmospheric concentrations of PM
10
and PM
2.5
in large cities causing a high
number of the exceedances of Air Quality Limit Values.
Discriminating source contributions within the road traffic sector is also of
importance for the health outcomes: low-contributing sources may be more relevant
to health. Heavy metals (such as Fe, Cu, Ba, Sb among others) originated by erosion
of brake and tyre materials and embedded in road dust induce oxidative stress.
Other toxic inorganic (sulphides; [
32
]) and organic (PAHs, [
104
]) compounds are
enriched in road dust particles. In California, a correlation between atmospheric
m
