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| Titel |
Modeling organic aerosols in a megacity: comparison of simple and complex representations of the volatility basis set approach |
| VerfasserIn |
M. Shrivastava, J. Fast, R. Easter, W. I. Gustafson, R. A. Zaveri, J. L. Jimenez, P. Saide, A. Hodzic |
| 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. 13 ; Nr. 11, no. 13 (2011-07-13), S.6639-6662 |
| Datensatznummer |
250009908
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| Publikation (Nr.) |
 copernicus.org/acp-11-6639-2011.pdf |
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| Zusammenfassung |
| The Weather Research and Forecasting model coupled with chemistry (WRF-Chem)
is modified to include a volatility basis set (VBS) treatment of secondary
organic aerosol formation. The VBS approach, coupled with SAPRC-99 gas-phase
chemistry mechanism, is used to model gas-particle partitioning and multiple
generations of gas-phase oxidation of organic vapors. In addition to the
detailed 9-species VBS, a simplified mechanism using 2 volatility species
(2-species VBS) is developed and tested for similarity to the 9-species VBS
in terms of both mass and oxygen-to-carbon ratios of organic aerosols in the
atmosphere. WRF-Chem results are evaluated against field measurements of
organic aerosols collected during the MILAGRO 2006 campaign in the vicinity
of Mexico City. The simplified 2-species mechanism reduces the computational
cost by a factor of 2 as compared to 9-species VBS. Both ground site and
aircraft measurements suggest that the 9-species and 2-species VBS
predictions of total organic aerosol mass as well as individual organic
aerosol components including primary, secondary, and biomass burning are
comparable in magnitude. In addition, oxygen-to-carbon ratio predictions
from both approaches agree within 25 %, providing evidence that the
2-species VBS is well suited to represent the complex evolution of organic
aerosols. Model sensitivity to amount of anthropogenic semi-volatile and
intermediate volatility (S/IVOC) precursor emissions is also examined by
doubling the default emissions. Both the emission cases significantly
under-predict primary organic aerosols in the city center and along aircraft
flight transects. Secondary organic aerosols are predicted reasonably well
along flight tracks surrounding the city, but are consistently
over-predicted downwind of the city. Also, oxygen-to-carbon ratio
predictions are significantly improved compared to prior studies by adding
15 % oxygen mass per generation of oxidation; however, all modeling cases
still under-predict these ratios downwind as compared to measurements,
suggesting a need to further improve chemistry parameterizations of
secondary organic aerosol formation. |
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