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| Titel |
Gas/particle partitioning of water-soluble organic aerosol in Atlanta |
| VerfasserIn |
C. J. Hennigan, M. H. Bergin, A. G. Russell, A. Nenes, R. J. Weber |
| 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. 11 ; Nr. 9, no. 11 (2009-06-04), S.3613-3628 |
| Datensatznummer |
250007355
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| Publikation (Nr.) |
 copernicus.org/acp-9-3613-2009.pdf |
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| Zusammenfassung |
| Gas and particle-phase organic carbon compounds soluble in water (e.g., WSOC)
were measured simultaneously in Atlanta throughout the summer of 2007 to
investigate gas/particle partitioning of ambient secondary organic aerosol
(SOA). Previous studies have established that, in the absence of biomass
burning, particulate WSOC (WSOCp) is mainly from secondary organic
aerosol (SOA) production. Comparisons between WSOCp, organic carbon (OC)
and elemental carbon (EC) indicate that WSOCp was a nearly comprehensive
measure of SOA in the Atlanta summertime. WSOCp and gas-phase WSOC
(WSOCg) concentrations both exhibited afternoon maxima, indicating that
photochemistry was a major route for SOA formation. An additional nighttime
maximum in the WSOCg concentration indicated a dark source for oxidized
organic gases, but this was not accompanied by detectable increases in
WSOCp. To study SOA formation mechanisms, WSOC gas/particle partitioning
was investigated as a function of temperature, RH, NOx, O3, and
organic aerosol mass concentration. No clear relationship was observed
between temperature and partitioning, possibly due to a simultaneous effect
from other temperature-dependent processes. For example, positive temperature
effects on emissions of biogenic SOA precursors and photochemical SOA
formation may have accounted for the observed similar proportional increases
of WSOCp and WSOCg with temperature. Relative humidity data
indicated a linear dependence between partitioning and predicted fine
particle liquid water. Lower NOx concentrations were associated with
greater partitioning to particles, but WSOC partitioning had no visible
relation to O3 or fine particle OC mass concentration. There was,
however, a relationship between WSOC partitioning and the WSOCp concentration, suggesting a compositional dependence between
partitioning semi-volatile gases and the absorbing organic aerosol. Combined,
the overall results suggest two dominant SOA formation processes in urban
Atlanta during summer. One was the photochemical production of SOA from
presumably biogenic precursors that increased with the onset of sunrise and
peaked in the afternoon. The other, which showed no apparent diurnal pattern,
involved the partitioning of semi-volatile gases to liquid water, followed by
heterogeneous reactions. The co-emission of water vapor and biogenic VOCs
from vegetation may link these processes. |
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