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| Titel |
Stable carbon isotopes - an indicator for heterogeneous aging of organic aerosol? |
| VerfasserIn |
Ulrike Dusek, Rupert Holzinger, Thomas Röckmann |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043824
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| Zusammenfassung |
| Organic aerosol (OA) sources that derive from photosynthesis (such as biomass or fossil fuel
combustion) are usually depleted in 13C. Oxidative processing (aging) of the organic aerosol
can cause enrichment in aerosol 13C, if a significant amount of the oxidized compounds
evaporates from the aerosol.
We expose a series of aerosol samples from Ghent, Belgium to different temperatures in
an oven. We measure δ13C values and detailed organic chemistry on sub-fractions of OA that
are thermally desorbed at several 50 Ë C temperature steps ranging from 50 to 200 Ë C. For
carbon isotope analysis the compounds released at each temperature step are oxidized to CO2
using a platinum catalyst at 550 Ë C. The CO2 is then passed on to an isotope ratio mass
spectrometer (IRMS) to measure δ13C ratios. A part of the flow is diverted to an
aerosol Proton-Transfer-Reaction Mass Spectrometer (PT-RMS). This instrument is
able to resolve low volatility and highly oxygenated compounds that are virtually
inaccessible to other chemical classification. Here, we use the detailed chemical
information to derive O/C ratios for all organic sub-fractions released at different
temperatures.
Both δ13C values and O/C ratios increase with increasing oven temperature. Hence, less
volatile compounds that are released at higher temperatures contain more O and are enriched
in 13C compared to compounds released at lower temperatures. The increase of O/C ratios
with oven temperature is plausible, since the addition of an O containing functional group to
an organic molecule drastically decreases its vapour pressure. Interestingly, these more
oxidized compounds also show higher δ13C values, as could be expected from
heterogeneous aging processes. These should increase both the oxygen and the 13C
content of the organic fraction. This hypothesis is further substantiated by a strong
correlation of the 13C enrichment with the change of O/C ratios between 100 and
150 Ë C. At higher T this correlation does not exist, which might indicate sources
other than heterogeneous oxidation for the more highly oxygenated compounds. |
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