Error induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in regional chemical-transport models in urban environments
<p>We employed direct numerical simulations to estimate the error on chemical calculation in simulations with regional chemical-transport models induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in an urban boundary layer with strong and heterogeneously dis...
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Copernicus Publications
2021-01-01
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doaj-0c7c9f410c264fca96e1a0fb23ff0a962021-01-14T12:30:08ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242021-01-012148350310.5194/acp-21-483-2021Error induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in regional chemical-transport models in urban environmentsC. W. Y. Li0G. P. Brasseur1G. P. Brasseur2H. Schmidt3J. P. Mellado4Max Planck Institute for Meteorology, Bundesstrasse 53, 20146, Hamburg, GermanyMax Planck Institute for Meteorology, Bundesstrasse 53, 20146, Hamburg, GermanyNational Center for Atmospheric Research, 1850 Table Mesa Dr, Boulder, CO 80305, USAMax Planck Institute for Meteorology, Bundesstrasse 53, 20146, Hamburg, GermanyDepartment of Physics, Aerospace Engineering Division, Universitat Politècnica de Catalunya, C. Jordi Girona 1–3, 08034, Barcelona, Spain<p>We employed direct numerical simulations to estimate the error on chemical calculation in simulations with regional chemical-transport models induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in an urban boundary layer with strong and heterogeneously distributed surface emissions. In simulations of initially segregated reactive species with an entrainment-emission configuration with an A–B–C second-order chemical scheme, urban surface emission fluxes of the homogeneously emitted tracer A result in a very large segregation between the tracers and hence a very large overestimation of the effective chemical reaction rate in a complete-mixing model. This large effect can be indicated by a large Damköhler number (<span class="inline-formula"><i>D</i><i>a</i></span>) of the limiting reactant. With heterogeneous surface emissions of the two reactants, the resultant normalised boundary-layer-averaged effective chemical reaction rate is found to be in a Gaussian function of <span class="inline-formula"><i>D</i><i>a</i></span>, and it is increasingly overestimated by the imposed rate with an increased horizontal scale of emission heterogeneity. Coarse-grid models with resolutions commensurable to regional models give reduced yet still significant errors for all simulations with homogeneous emissions. Such model improvement is more sensitive to the increased vertical resolution. However, such improvement cannot be seen for simulations with heterogeneous emissions when the horizontal resolution of the model cannot resolve emission heterogeneity. This work highlights particular conditions in which the ability to resolve chemical segregation is especially important when modelling urban environments.</p>https://acp.copernicus.org/articles/21/483/2021/acp-21-483-2021.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
C. W. Y. Li G. P. Brasseur G. P. Brasseur H. Schmidt J. P. Mellado |
spellingShingle |
C. W. Y. Li G. P. Brasseur G. P. Brasseur H. Schmidt J. P. Mellado Error induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in regional chemical-transport models in urban environments Atmospheric Chemistry and Physics |
author_facet |
C. W. Y. Li G. P. Brasseur G. P. Brasseur H. Schmidt J. P. Mellado |
author_sort |
C. W. Y. Li |
title |
Error induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in regional chemical-transport models in urban environments |
title_short |
Error induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in regional chemical-transport models in urban environments |
title_full |
Error induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in regional chemical-transport models in urban environments |
title_fullStr |
Error induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in regional chemical-transport models in urban environments |
title_full_unstemmed |
Error induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in regional chemical-transport models in urban environments |
title_sort |
error induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in regional chemical-transport models in urban environments |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2021-01-01 |
description |
<p>We employed direct numerical simulations to estimate the error on chemical calculation in simulations with regional chemical-transport models induced by neglecting subgrid chemical segregation due to inefficient turbulent mixing in an urban boundary layer with strong and heterogeneously distributed surface emissions. In simulations of initially segregated reactive species with an entrainment-emission configuration with an A–B–C second-order chemical scheme, urban surface emission fluxes of the homogeneously emitted tracer A result in a very large segregation between the tracers and hence a very large overestimation of the effective chemical reaction rate in a complete-mixing model. This large effect can be indicated by a large Damköhler number (<span class="inline-formula"><i>D</i><i>a</i></span>) of the limiting reactant. With heterogeneous surface emissions of the two reactants, the resultant normalised boundary-layer-averaged effective chemical reaction rate is found to be in a Gaussian function of <span class="inline-formula"><i>D</i><i>a</i></span>, and it is increasingly overestimated by the imposed rate with an increased horizontal scale of emission heterogeneity. Coarse-grid models with resolutions commensurable to regional models give reduced yet still significant errors for all simulations with homogeneous emissions. Such model improvement is more sensitive to the increased vertical resolution. However, such improvement cannot be seen for simulations with heterogeneous emissions when the horizontal resolution of the model cannot resolve emission heterogeneity. This work highlights particular conditions in which the ability to resolve chemical segregation is especially important when modelling urban environments.</p> |
url |
https://acp.copernicus.org/articles/21/483/2021/acp-21-483-2021.pdf |
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