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| Titel |
Simulations of organic aerosol concentrations in Mexico City using the WRF-CHEM model during the MCMA-2006/MILAGRO campaign |
| VerfasserIn |
G. Li, M. Zavala, W. Lei, A. P. Tsimpidi, V. A. Karydis, S. N. Pandis, M. R. Canagaratna, L. T. Molina |
| 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. 8 ; Nr. 11, no. 8 (2011-04-27), S.3789-3809 |
| Datensatznummer |
250009650
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| Publikation (Nr.) |
 copernicus.org/acp-11-3789-2011.pdf |
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| Zusammenfassung |
| Organic aerosol concentrations are simulated using the
WRF-CHEM model in Mexico City during the period from 24 to 29 March in association with the MILAGRO-2006 campaign. Two approaches are
employed to predict the variation and spatial distribution of the organic
aerosol concentrations: (1) a traditional 2-product secondary organic aerosol
(SOA) model with non-volatile primary organic aerosols (POA); (2) a
non-traditional SOA model including the volatility basis-set modeling method
in which primary organic components are assumed to be semi-volatile and
photochemically reactive and are distributed in logarithmically spaced
volatility bins. The MCMA (Mexico City Metropolitan Area) 2006 official
emission inventory is used in simulations and the POA emissions are modified
and distributed by volatility based on dilution experiments for the
non-traditional SOA model. The model results are compared to the Aerosol
Mass Spectrometry (AMS) observations analyzed using the Positive Matrix
Factorization (PMF) technique at an urban background site (T0) and a
suburban background site (T1) in Mexico City. The traditional SOA model
frequently underestimates the observed POA concentrations during rush hours
and overestimates the observations in the rest of the time in the city. The
model also substantially underestimates the observed SOA concentrations,
particularly during daytime, and only produces 21% and 25% of the
observed SOA mass in the suburban and urban area, respectively. The
non-traditional SOA model performs well in simulating the POA variation, but
still overestimates during daytime in the urban area. The SOA simulations
are significantly improved in the non-traditional SOA model compared to the
traditional SOA model and the SOA production is increased by more than
100% in the city. However, the underestimation during daytime is still
salient in the urban area and the non-traditional model also fails to
reproduce the high level of SOA concentrations in the suburban area. In the
non-traditional SOA model, the aging process of primary organic components
considerably decreases the OH levels in simulations and further impacts the
SOA formation. If the aging process in the non-traditional model does not
have feedback on the OH in the gas-phase chemistry, the SOA production is
enhanced by more than 10% compared to the simulations with the OH
feedback during daytime, and the gap between the simulations and
observations in the urban area is around 3 μg m−3 or 20% on
average during late morning and early afternoon, within the uncertainty from
the AMS measurements and PMF analysis. In addition, glyoxal and
methylglyoxal can contribute up to approximately 10% of the observed SOA
mass in the urban area and 4% in the suburban area. Including the non-OH
feedback and the contribution of glyoxal and methylglyoxal, the
non-traditional SOA model can explain up to 83% of the observed SOA in
the urban area, and the underestimation during late morning and early
afternoon is reduced to 0.9 μg m−3 or 6% on average.
Considering the uncertainties from measurements, emissions, meteorological
conditions, aging of semi-volatile and intermediate volatile organic
compounds, and contributions from background transport, the non-traditional
SOA model is capable of closing the gap in SOA mass between measurements and
models. |
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