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| Titel |
Secondary Organic Aerosol Formation from Acetylene (C2H2): seed effect on SOA yields due to organic photochemistry in the aerosol aqueous phase |
| VerfasserIn |
R. Volkamer, P. J. Ziemann, M. J. Molina |
| 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 ; 9, no. 6 ; Nr. 9, no. 6 (2009-03-19), S.1907-1928 |
| Datensatznummer |
250007084
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| Publikation (Nr.) |
 copernicus.org/acp-9-1907-2009.pdf |
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| Zusammenfassung |
| The lightest Non Methane HydroCarbon (NMHC), i.e., acetylene
(C2H2) is found to form secondary organic aerosol (SOA). Contrary
to current belief, the number of carbon atoms, n, for a NMHC to act as SOA
precursor is lowered to n=2 here. The OH-radical initiated oxidation of
C2H2 forms glyoxal (CHOCHO) as the highest yield product, and
>99% of the SOA from C2H2 is attributed to CHOCHO. SOA
formation from C2H2 and CHOCHO was studied in a photochemical and
a dark simulation chamber. Further, the experimental conditions were varied
with respect to the chemical composition of the seed aerosols, mild
acidification with sulphuric acid (SA, 3<pH<4), and relative humidity
(10<RH<90%). The rate of SOA formation is found enhanced by several
orders of magnitude in the photochemical system. The SOA yields (YSOA)
ranged from 1% to 24% and did not correlate with the organic mass
portion of the seed, but increased linearly with liquid water content (LWC)
of the seed. For fixed LWC, YSOA varied by more than a factor of five.
Water soluble organic carbon (WSOC) photochemistry in the liquid water
associated with internally mixed inorganic/WSOC seed aerosols is found
responsible for this seed effect. WSOC photochemistry enhances the SOA
source from CHOCHO, while seeds containing amino acids (AA) and/or SA showed
among the lowest of all YSOA values, and largely suppress the
photochemical enhancement on the rate of CHOCHO uptake. Our results give
first evidence for the importance of heterogeneous photochemistry of CHOCHO
in SOA formation, and identify a potential bias in the currently available
YSOA data for other SOA precursor NMHCs. We demonstrate that SOA
formation via the aqueous phase is not limited to cloud droplets, but
proceeds also in the absence of clouds, i.e., does not stop once a cloud
droplet evaporates. Atmospheric models need to be expanded to include SOA
formation from WSOC photochemistry of CHOCHO, and possibly other α-dicarbonyls, in aqueous aerosols. |
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