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| Titel |
Simulating the oxygen content of ambient organic aerosol with the 2D volatility basis set |
| VerfasserIn |
B. N. Murphy, N. M. Donahue, C. Fountoukis, 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. 15 ; Nr. 11, no. 15 (2011-08-04), S.7859-7873 |
| Datensatznummer |
250009979
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| Publikation (Nr.) |
 copernicus.org/acp-11-7859-2011.pdf |
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| Zusammenfassung |
| A module predicting the oxidation state of organic aerosol (OA) has been
developed using the two-dimensional volatility basis set (2D-VBS) framework.
This model is an extension of the 1D-VBS framework and tracks saturation
concentration and oxygen content of organic species during their atmospheric
lifetime. The host model, a one-dimensional Lagrangian transport model, is
used to simulate air parcels arriving at Finokalia, Greece during the
Finokalia Aerosol Measurement Experiment in May 2008 (FAME-08). Extensive
observations were collected during this campaign using an aerosol mass
spectrometer (AMS) and a thermodenuder to determine the chemical composition
and volatility, respectively, of the ambient OA. Although there are several
uncertain model parameters, the consistently high oxygen content of OA
measured during FAME-08 (O:C = 0.8) can help constrain these parameters and
elucidate OA formation and aging processes that are necessary for achieving
the high degree of oxygenation observed. The base-case model reproduces
observed OA mass concentrations (measured mean = 3.1 μg m−3,
predicted mean = 3.3 μg m−3) and O:C (predicted O:C = 0.78)
accurately. A suite of sensitivity studies explore uncertainties due to (1)
the anthropogenic secondary OA (SOA) aging rate constant, (2) assumed
enthalpies of vaporization, (3) the volatility change and number of oxygen
atoms added for each generation of aging, (4) heterogeneous chemistry, (5) the
oxidation state of the first generation of compounds formed from SOA
precursor oxidation, and (6) biogenic SOA aging. Perturbations in most of
these parameters do impact the ability of the model to predict O:C well
throughout the simulation period. By comparing measurements of the O:C from
FAME-08, several sensitivity cases including a high oxygenation case, a low
oxygenation case, and biogenic SOA aging case are found to unreasonably
depict OA aging, keeping in mind that this study does not consider possibly
important processes like fragmentation that may offset mass gains and affect
the prediction bias. On the other hand, many of the cases chosen for this
study predict average O:C estimates that are consistent with the
observations, illustrating the need for more thorough experimental
characterizations of OA parameters including the enthalpy of vaporization
and oxidation state of the first generation of SOA products. The ability of
the model to predict OA concentrations is less sensitive to perturbations in
the model parameters than its ability to predict O:C. In this sense, quantifying O:C with a predictive model and
constraining it with AMS measurements can reduce uncertainty in our
understanding of OA formation and aging. |
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