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| Titel |
A high-order size-resolved ultrafine particle model for a traffic tunnel |
| VerfasserIn |
Peter Vos, Irina Nikolova, Stijn Janssen |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052549
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| Zusammenfassung |
| Motivation
Ultrafine particles Ultrafine particles (UFP) are the smallest constituents of
airborne particulate matter and are typically low in mass but high in number.
There is increasing scientific evidence that (traffic related) ultrafine particles may
be more harmful to health than the coarser particles which account for most of
the mass in the regulated PM10 and PM2.5 fractions [1].
A tunnel model No consensus has been reached whether UFP transformation
processes (such as deposition, coagulation, condensation) should be taken into
account for appropriately modelling the dispersion of UFP [2]. Due to their
confined space and the controlled conditions, traffic tunnels form the ideal
environment to investigate this hypothesis.
The model
The presented UFP tunnel model consists of a number of modules that implement the
most important transport and transformation processes, i.e. emissions, advection,
deposition, coagulation, condensation. The model calculates a continuous UFP number
distribution at every location inside the tunnel (assuming a uniform concentration along
every cross section). Despite its resemblance with existing Aerosol Box Models, the
presented UFP tunnel model differs from existing models in the following sense:
A continuous description Most UFP models employ a discrete representation
of the solution (e.g. by using the size bin approach) based upon the discrete
formulation of the General Dynamic Equation. We start from the continuous
formulation and use corresponding numerical methods.
High-accurate state-of-the-art numerical methods We have combined the
Discontinuous Galerkin method with a high-order spectral element approach
(typically up to 12th order). Such high-order methods are known to yield
high-accurate solutions.
A fully size-resolved approach Next to a size-resolved description of the
solution, we have also adopted a fully size-dependent description of the various
transformation processes. As such, as well the deposition speed, the coagulation
coefficient as the condensation rate do depend on the particle size.
A two-dimensional model Aerosol dynamics box-models generally only
depend on the particle size. The presented model calculates the UFP
concentration in function of the particle size and the (axial) position inside
the tunnel. As result, the model can be classified as a two-dimensional
time-dependent model.
Results
Next to the presentation of the model, we also plan to elaborate on
The validation of the model A typical bottleneck in UFP dispersion modelling
is the lack of size-resolved measurement data for model validation. We have
validated our model by means of the results of a very recent road-tunnel
size-resolved UFP measurement campaign [3].
The estimation of emission factors The presented model allows us to
back-calculate emission factors from measurements, as well as comparing these
results to existing emission models.
The identification of the relevant UFP transformation processes The use of
a continuous representation of the solution together with a high-order numerical
method allows us to accurately identify the transformation processes that
significantly affect the dispersion of UFP inside a traffic tunnel. We will present
the results of the corresponding size-resolved time-scale analysis.
References
[1]Â Â Â Oberdörster, G., Oberdörster, E., Oberdörster, J., Nanotoxicology: an emerging
discipline evolving from studies of ultrafine particles. Environ. Health Perspect.,
113(7), 823–839, 2005
[2]Â Â Â Kumar, P., Robins, A., Vardoulakis, S. and Britter, R., A review of the
characteristics of nanoparticles in the urban atmosphere and the prospects for
developing regulatory controls, Atmos. Environ., 44(39), 5035-5052, 2010
[3]Â Â Â Cheng, Y. H., Liu, Z. S., Chen, C. C., On-road measurements of ultrafine
particle concentration profiles and their size distributions inside the longest
highway tunnel in Southeast Asia. Atmos. Environ., 44(6), 763-772, 2010 |
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