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| Titel |
The influence of semi-volatile and reactive primary emissions on the abundance and properties of global organic aerosol |
| VerfasserIn |
S. H. Jathar, S. C. Farina, A. L. Robinson, P. J. Adams |
| 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 (2011-08-03), S.7727-7746 |
| Datensatznummer |
250009972
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| Publikation (Nr.) |
 copernicus.org/acp-11-7727-2011.pdf |
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| Zusammenfassung |
| Semi-volatile and reactive primary organic aerosols are modeled on a global
scale using the GISS GCM II' "unified" climate model. We employ the
volatility basis set framework to simulate emissions, chemical reactions and
phase partitioning of primary and secondary organic aerosol (POA and SOA).
The model also incorporates the emissions and reactions of intermediate
volatility organic compounds (IVOCs) as a source of organic aerosol (OA), one
that has been missing in most prior work. Model predictions are evaluated
against a broad set of observational constraints including mass
concentrations, degree of oxygenation, volatility and isotopic composition. A
traditional model that treats POA as non-volatile and non-reactive is also
compared to the same set of observations to highlight the progress made in
this effort. The revised model predicts a global dominance of SOA and brings
the POA/SOA split into better agreement with ambient measurements. This
change is due to traditionally defined POA evaporating and the evaporated
vapors oxidizing to form non-traditional SOA. IVOCs (traditionally not
included in chemical transport models) oxidize to form condensable products
that account for a third of total OA, suggesting that global models have been
missing a large source of OA. Predictions of the revised model for the SOA
fraction at 17 different locations compared much better to observations than
predictions from the traditional model. Model-predicted volatility is
compared with thermodenuder data collected at three different different field campaigns:
FAME-2008, MILAGRO-2006 and SOAR-2005. The revised model predicts the OA
volatility much more closely than the traditional model. When compared
against monthly averaged OA mass concentrations measured by the IMPROVE
network, predictions of the revised model lie within a
factor of two in summer and mostly within a factor of five during winter. A
sensitivity analysis indicates that the winter comparison can be improved
either by increasing POA emissions or lowering the volatility of those
emissions. Model predictions of the isotopic composition of OA are compared
against those computed via a radiocarbon isotope analysis of field samples.
The contemporary fraction, on average, is slightly under-predicted (20 %)
during the summer months but is a factor of two lower during the winter
months. We hypothesize that the large wintertime under-prediction of surface
OA mass concentrations and the contemporary fraction is due to an
under-representation of biofuel (particularly, residential wood burning)
emissions in the emissions inventory. Overall, the model evaluation highlights
the importance of treating POA as semi-volatile and reactive in order to
predict accurately the sources, composition and properties of ambient OA. |
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