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| Titel |
Sources and production of organic aerosol in Mexico City: insights from the combination of a chemical transport model (PMCAMx-2008) and measurements during MILAGRO |
| VerfasserIn |
A. P. Tsimpidi, V. A. Karydis, M. Zavala, W. Lei, N. Bei, L. Molina, S. N. Pandis |
| 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. 11 ; Nr. 11, no. 11 (2011-06-01), S.5153-5168 |
| Datensatznummer |
250009794
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| Publikation (Nr.) |
 copernicus.org/acp-11-5153-2011.pdf |
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| Zusammenfassung |
| Urban areas are large sources of organic aerosols and their precursors.
Nevertheless, the contributions of primary (POA) and secondary organic
aerosol (SOA) to the observed particulate matter levels have been difficult
to quantify. In this study the three-dimensional chemical transport model
PMCAMx-2008 is used to investigate the temporal and geographic variability
of organic aerosol in the Mexico City Metropolitan Area (MCMA) during the
MILAGRO campaign that took place in the spring of 2006. The organic module
of PMCAMx-2008 includes the recently developed volatility basis-set
framework in which both primary and secondary organic components are assumed
to be semi-volatile and photochemically reactive and are distributed in
logarithmically spaced volatility bins. The MCMA emission inventory is
modified and the POA emissions are distributed by volatility based on
dilution experiments. The model predictions are compared with observations
from four different types of sites, an urban (T0), a suburban (T1), a rural
(T2), and an elevated site in Pico de Tres Padres (PTP). The performance of
the model in reproducing organic mass concentrations in these sites is
encouraging. The average predicted PM1 organic aerosol (OA) concentration in T0, T1, and
T2 is 18 μg m−3, 11.7 μg m−3, and 10.5 μg m−3
respectively, while the corresponding measured values are
17.2 μg m−3, 11 μg m−3, and 9 μg m−3. The average
predicted locally-emitted primary OA concentrations, 4.4 μg m−3 at
T0, 1.2 μg m−3 at T1 and 1.7 μg m−3 at PTP, are in
reasonably good agreement with the corresponding PMF analysis estimates
based on the Aerosol Mass Spectrometer (AMS) observations of 4.5, 1.3, and
2.9 μg m−3 respectively. The model reproduces reasonably well the
average oxygenated OA (OOA) levels in T0 (7.5 μg m−3 predicted
versus 7.5 μg m−3 measured), in T1 (6.3 μg m−3 predicted
versus 4.6 μg m−3 measured) and in PTP (6.6 μg m−3
predicted versus 5.9 μg m−3 measured). The rest of the OA mass
(6.1 μg m−3 and 4.2 μg m−3 in T0 and T1 respectively) is
assumed to originate from biomass burning activities and is introduced to
the model as part of the boundary conditions. Inside Mexico City (at T0),
the locally-produced OA is predicted to be on average 60 % locally-emitted
primary (POA), 6 % semi-volatile (S-SOA) and intermediate volatile (I-SOA)
organic aerosol, and 34 % traditional SOA from the oxidation of VOCs
(V-SOA). The average contributions of the OA components to the
locally-produced OA for the entire modelling domain are predicted to be
32 % POA, 10 % S-SOA and I-SOA, and 58 % V-SOA. The long range
transport from biomass burning activities and other sources in Mexico is
predicted to contribute on average almost as much as the local sources
during the MILAGRO period. |
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