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| Titel |
On the segregation of chemical species in a clear boundary layer over heterogeneous land surfaces |
| VerfasserIn |
H. G. Ouwersloot, J. Vilà-Guerau de Arellano, C. C. Heerwaarden, L. N. Ganzeveld, M. C. Krol, J. Lelieveld  |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 20 ; Nr. 11, no. 20 (2011-10-28), S.10681-10704 |
| Datensatznummer |
250010152
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| Publikation (Nr.) |
 copernicus.org/acp-11-10681-2011.pdf |
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| Zusammenfassung |
| Using a Large-Eddy Simulation model, we have systematically studied the inability of boundary layer turbulence to
efficiently mix reactive species. This creates regions where the species are
accumulated in a correlated or anti-correlated way, thereby modifying the
mean reactivity. We quantify this modification by the intensity of
segregation, IS, and analyse the driving mechanisms: heterogeneity
of the surface moisture and heat fluxes, various background wind patterns and
non-uniform isoprene emissions. The heterogeneous surface conditions are characterized by cool
and wet forested patches with high isoprene emissions, alternated
with warm and dry patches that represents pasture with relatively low
isoprene emissions. For typical conditions in the Amazon rain
forest, applying homogeneous surface forcings and in the absence of free tropospheric NOx, the isoprene-OH reaction rate
is altered by less than 10%. This is substantially smaller than the
previously assumed IS of 50% in recent large-scale model
analyses of tropical rain forest chemistry. Spatial heterogeneous surface
emissions enhance the segregation of species, leading to alterations of the
chemical reaction rates up to 20%. The intensities of segregation are enhanced when the
background wind direction is parallel to the borders between the patches and
reduced in the case of a perpendicular wind direction. The effects of segregation
on trace gas concentrations vary per species. For the highly reactive OH, the
differences in concentration averaged over the boundary layer are less than
2% compared to homogeneous surface conditions, while the isoprene
concentration is increased by as much as 12% due to the reduced chemical
reaction rates. These processes take place at the sub-grid scale of chemistry
transport models and therefore need to be parameterized. |
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