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| Titel |
Formation of anthropogenic secondary organic aerosol (SOA) and its influence on biogenic SOA properties |
| VerfasserIn |
E. U. Emanuelsson, M. Hallquist, K. Kristensen, M. Glasius, B. Bohn, H. Fuchs, B. Kammer, A. Kiendler-Scharr, S. Nehr, F. Rubach, R. Tillmann, A. Wahner, H.-C. Wu, Th. F. Mentel |
| 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 ; 13, no. 5 ; Nr. 13, no. 5 (2013-03-11), S.2837-2855 |
| Datensatznummer |
250018486
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| Publikation (Nr.) |
 copernicus.org/acp-13-2837-2013.pdf |
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| Zusammenfassung |
| Secondary organic aerosol (SOA) formation from mixed anthropogenic and
biogenic precursors has been studied exposing reaction mixtures to natural
sunlight in the SAPHIR chamber in Jülich, Germany. In this study
aromatic compounds served as examples of anthropogenic volatile organic
compound (VOC) and a mixture of α-pinene and limonene as an example
for biogenic VOC. Several experiments with exclusively aromatic precursors
were performed to establish a relationship between yield and organic aerosol
mass loading for the atmospheric relevant range of aerosol loads of 0.01 to
10 μg m−3. The yields (0.5 to 9%) were comparable to previous
data and further used for the detailed evaluation of the mixed biogenic and
anthropogenic experiments. For the mixed experiments a number of different
oxidation schemes were addressed. The reactivity, the sequence of addition,
and the amount of the precursors influenced the SOA properties. Monoterpene
oxidation products, including carboxylic acids and dimer esters were
identified in the aged aerosol at levels comparable to ambient air. OH
radicals were measured by Laser Induced Fluorescence, which allowed for
establishing relations of aerosol properties and composition to the
experimental OH dose. Furthermore, the OH measurements in combination with
the derived yields for aromatic SOA enabled application of a simplified
model to calculate the chemical turnover of the aromatic precursor and
corresponding anthropogenic contribution to the mixed aerosol. The estimated
anthropogenic contributions were ranging from small (≈8%) up to
significant fraction (>50%) providing a suitable range to
study the effect of aerosol composition on the aerosol volatility (volume
fraction remaining (VFR) at 343 K: 0.86–0.94). The aromatic aerosol had
higher oxygen to carbon ratio O/C and was less volatile than the biogenic
fraction. However, in order to produce significant amount of aromatic SOA
the reaction mixtures needed a higher OH dose that also increased O/C and
provided a less volatile aerosol. The SOA yields, O/C, and f44 (the mass
fraction of CO2+ ions in the mass spectra which can be considered
as a measure of carboxylic groups) in the mixed photo-chemical experiments
could be described as linear combinations of the corresponding properties of
the pure systems. For VFR there was in addition an enhancement effect,
making the mixed aerosol significantly less volatile than what could be
predicted from the pure systems. A strong positive correlation was found
between changes in volatility and O/C with the exception during dark hours
where the SOA volatility decreased while O/C did not change significantly.
Thus, this change in volatility under dark conditions as well as the
anthropogenic enhancement is due to chemical or morphological changes not
affecting O/C. |
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