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| Titel |
Modeling anthropogenically controlled secondary organic aerosols in a megacity: a simplified framework for global and climate models |
| VerfasserIn |
A. Hodzic, J. L. Jimenez |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 4, no. 4 ; Nr. 4, no. 4 (2011-10-24), S.901-917 |
| Datensatznummer |
250001912
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| Publikation (Nr.) |
 copernicus.org/gmd-4-901-2011.pdf |
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| Zusammenfassung |
| A simplified parameterization for secondary organic aerosol (SOA) formation
in polluted air and biomass burning smoke is tested and optimized in this
work, towards the goal of a computationally inexpensive method to calculate
pollution and biomass burning SOA mass and hygroscopicity in global and
climate models. A regional chemistry-transport model is used as the testbed
for the parameterization, which is compared against observations from the
Mexico City metropolitan area during the MILAGRO 2006 field experiment. The
empirical parameterization is based on the observed proportionality of SOA
concentrations to excess CO and photochemical age of the airmass. The
approach consists in emitting an organic gas as lumped SOA precursor
surrogate proportional to anthropogenic or biomass burning CO emissions
according to the observed ratio between SOA and CO in aged air, and reacting
this surrogate with OH into a single non-volatile species that condenses to
form SOA. An emission factor of 0.08 g of the lumped SOA precursor per g of
CO and a rate constant with OH of 1.25 × 10−11 cm3 molecule−1 s−1 reproduce the observed average SOA mass within 30 % in the urban
area and downwind. When a 2.5 times slower rate is used (5 × 10−12 cm3 molecule−1 s−1) the predicted SOA amount and temporal
evolution is nearly identical to the results obtained with SOA formation
from semi-volatile and intermediate volatility primary organic vapors
according to the Robinson et al. (2007) formulation. Our simplified method
has the advantage of being much less computationally expensive than
Robinson-type methods, and can be used in regions where the emissions of SOA
precursors are not yet available. As the aged SOA/ΔCO
ratios are rather consistent globally for anthropogenic pollution, this parameterization could be
reasonably tested in and applied to other regions. The evolution of
oxygen-to-carbon ratio was also empirically modeled and the predicted levels
were found to be in reasonable agreement with observations. The potential
enhancement of biogenic SOA by anthropogenic pollution, which has been
suggested to play a major role in global SOA formation, is also tested using
two simple parameterizations. Our results suggest that the pollution
enhancement of biogenic SOA could provide
additional SOA, but does not however explain the concentrations or the
spatial and temporal variations of measured SOA mass in the vicinity of
Mexico City, which appears to be controlled by anthropogenic sources. The
contribution of the biomass burning to the predicted SOA is less than 10%
during the studied period. |
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