Environmental Engineering Reference
In-Depth Information
(i.e. the side of road) on the number of particles measured, may imply that the
process is not primarily driven by wind dispersion but by turbulence.
The third possibility is that due to high local concentrations and turbulence during
peaks, particles collide and coagulate thus reducing the number of particles but not
the mass. This assumption will be tested in a future experiment.
Simplified dispersion models can be used to demonstrate that under stable meteo-
rological conditions, as was the case during our study, dispersion over short ranges
is only determined by distance and the initial mixing volume which depends on the
size and wake of the vehicles. This is entirely consistent with our measurements.
Further studies are required to corroborate the tentative conclusions of this
experiment. In this paper we have focused on mobile measurements in real traffic
because these are most relevant for exposure of UFP to cyclists, and also of interest
to policy makers. Unfortunately the GPS readings are not accurate enough to deter-
mine the exact distance between the emission and the P-TRAK sampling tube.
To test which explanation effect best accounts for the measurements, we will use
fixed monitors at different distances from the road, measuring both UFP and PM
mass. In addition, this will allow us to confirm the results for different wind speeds
and directions and determine the rate of decrease at different distances. This decay
function will then be used to construct a CFD model in ENVI-met ( www.envi-met.
com ) that will allow us to make more general predictions as well as study scenarios
that may modify exposure of UFP on the cycling track (such as separation distance,
provision of physical separation by parked cars, sound screens or green hedges) [5, 6] .
True exposure to cyclists should be defined as a combination of concentrations and
inhalation. Therefore (in other parallel experiments) simultaneous measurements are
taken of physical load (breathing rate, oxygen consumption and power output). These
combined measurements will allow us to determine the exact quantity of particulate
matter that is inhaled. This quantity is important to determine accurately because in
the end it determines whether cyclists are exposed to a higher internal dose of PM
than car drivers are. No other project has ever designed such simultaneous measure-
ments and most authors have either used rough estimates to account for the higher
breathing rate of cyclists [4] or used modeled PM levels [7] . Given that the ultimate
goal of the SHAPES project is to provide conclusions and recommendations for all
Belgian regions, it is important to take the effects of slopes on breathing rate into
account. All test trajectories therefore include sections with slopes.
Conclusion
A P-TRAK device can conveniently be used for making UFP measurements
while cycling. UFP measurements prove to be a very useful supplement to PM10
and PM2.5 measurements as they are more closely related to emissions of
motorized traffic.
Measurements show that at least under some conditions UFP fall rapidly
with increasing distances from the emission source. This reveals important new
Search WWH ::




Custom Search