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| Titel |
Dimers in α-pinene secondary organic aerosol: effect of hydroxyl radical, ozone, relative humidity and aerosol acidity |
| VerfasserIn |
K. Kristensen, T. Cui, H. Zhang, A. Gold, M. Glasius, J. D. Surratt |
| 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 ; 14, no. 8 ; Nr. 14, no. 8 (2014-04-28), S.4201-4218 |
| Datensatznummer |
250118641
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| Publikation (Nr.) |
 copernicus.org/acp-14-4201-2014.pdf |
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| Zusammenfassung |
The formation of secondary organic aerosol (SOA) from both ozonolysis and
hydroxyl radical (OH)-initiated oxidation of α-pinene under
conditions of high nitric oxide (NO) concentrations with varying relative
humidity (RH) and aerosol acidity was investigated in the University of
North Carolina dual outdoor smog chamber facility. SOA formation from
ozonolysis of α-pinene was enhanced relative to that from
OH-initiated oxidation in the presence of initially high-NO conditions.
However, no effect of RH on SOA mass was evident. Ozone (O3)-initiated
oxidation of α-pinene in the presence of ammonium sulfate (AS) seed
coated with organic aerosol from OH-initiated oxidation of α-pinene
showed reduced nucleation compared to ozonolysis in the presence of pure AS
seed aerosol.
The chemical composition of α-pinene SOA was investigated by
ultra-performance liquid chromatography/electrospray ionization
high-resolution quadrupole time-of-flight mass spectrometry
(UPLC/ESI-HR-Q-TOFMS), with a focus on the formation of carboxylic acids and
high-molecular weight dimers. A total of eight carboxylic acids and four
dimers were identified, constituting between 8 and 12% of the total
α-pinene SOA mass. OH-initiated oxidation of α-pinene in the
presence of nitrogen oxides (NOx) resulted in the formation of highly
oxidized carboxylic acids, such as 3-methyl-1,2,3-butanetricarboxylic acid
(MBTCA) and diaterpenylic acid acetate (DTAA). The formation of dimers was
observed only in SOA produced from the ozonolysis of α-pinene in the
absence of NOx, with increased concentrations by a factor of two at
higher RH (50–90%) relative to lower RH (30–50%). The increased
formation of dimers correlates with an observed increase in new particle
formation at higher RH due to nucleation. Increased aerosol acidity was
found to have a negligible effect on the formation of the dimers. SOA mass
yield did not influence the chemical composition of SOA formed from α-pinene ozonolysis with respect to carboxylic acids and dimers.
The results support the formation of the high-molecular weight dimers
through gas-phase reactions of the stabilized Criegee Intermediate (sCI)
formed from the ozonolysis of α-pinene. The high molecular weight
and polar nature of dimers formed in the gas phase may explain increased
particle number concentration as a result of homogenous nucleation. Since
three of these dimers (i.e. pinyl-diaterpenyl dimer (MW 358),
pinyl-diaterebyl dimer (MW 344) and pinonyl-pinyl dimer (MW 368)) have been
observed in both laboratory-generated and ambient fine organic aerosol
samples, we conclude that the dimers observed in this study can be used as
tracers for the O3-initiated oxidation of α-pinene, and are
therefore indicative of enhanced anthropogenic activities, and that the high
molecular weight and low volatility dimers result in homogenous nucleation
under laboratory conditions, increasing the particle number concentration. |
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