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| Titel |
Dry deposition modelling of air pollutants over urban areas |
| VerfasserIn |
N. Cherin, Y. Roustan, C. Seigneur, L. Musson Genon |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067517
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| Zusammenfassung |
| More than one-half of the world’s inhabitants lives in urban areas. Consequently, the
evolution of pollutants inside these urban areas are problems of great concern in air quality
studies. Though the dry deposition fluxes of air pollutants, which are known to be significant
in the neighborhood of sources of pollution, like urban areas, have not been modeled
precisely until recently within urban areas.
By reviewing the physics of the processes leading to the dry deposition of air pollutants, it
is clear that atmosphere turbulence is crucial for dry deposition. Urban areas, and particularly
buildings, are known to significantly impact flow fields and then by extension the dry
deposition fluxes. Numerous urban schemes have been developed in the past decades to
approximate the effect of the local scale urban elements on drag, heat flux and radiative
budget. The most recent urban canopy models are based on quite simple geometries,
but sufficiently close to represent the aerodynamic and thermal characteristics of
cities.
These canopy models are generally intended to parameterize aerodynamic and thermal
fields, but not dry deposition. For dry deposition, the current classical “roughness” approach,
uses only two representative parameters, z0 and d, namely the roughness length and the
zero-plane displacement height to represent urban areas. In this work, an innovative dry
deposition model based on the urban canyon concept, is proposed. It considers a single road,
bordered by two facing buildings, which are treated separately. It accounts for sub-grid
effects of cities, especially a better parameterization of the turbulence scheme, through the
use of local mixing length and a more detailled description of the urban area and key
parameters within the urban canopy. Three different flow regimes are distinguished in the
urban canyon according to the height-to-width ratio: isolated roughness flow, wake
interference flow and skimming flow regime. The magnitude of differences in dry deposition
fields between both classical “roughness” model and the more complete model developed
here is investigated. For instance, the dry deposition fluxes are underestimated by the new
model in comparison to the classical one during the day, but are overestimated during
the night. This approach also provides spatially segregated dry deposition fields
within the urban area which cannot be obtained from the classical “roughness”
approach. |
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