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| Titel |
Hydrocarbon-like and oxygenated organic aerosols in Pittsburgh: insights into sources and processes of organic aerosols |
| VerfasserIn |
Q. Zhang, D. R. Worsnop, M. R. Canagaratna, J. L. Jimenez |
| 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 ; 5, no. 12 ; Nr. 5, no. 12 (2005-12-14), S.3289-3311 |
| Datensatznummer |
250003194
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| Publikation (Nr.) |
 copernicus.org/acp-5-3289-2005.pdf |
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| Zusammenfassung |
| A recently developed algorithm (Zhang et al., 2005) has been applied to deconvolve the mass spectra of
organic aerosols acquired with the Aerosol Mass Spectrometer (AMS) in
Pittsburgh during September 2002. The results are used here to characterize
the mass concentrations, size distributions, and mass spectra of
hydrocarbon-like and oxygenated organic aerosol (HOA and OOA, respectively).
HOA accounts for 34% of the measured organic aerosol mass and OOA
accounts for 66%. The mass concentrations of HOA demonstrate a prominent
diurnal profile that peaks in the morning during the rush hour and decreases
with the rise of the boundary layer. The diurnal profile of OOA is
relatively flat and resembles those of SO42− and NH4+.
The size distribution of HOA shows a distinct ultrafine mode that is
commonly associated with fresh emissions while OOA is generally concentrated
in the accumulation mode and appears to be mostly internally mixed with the
inorganic ions, such as SO42− and NH4+. These
observations suggest that HOA is likely primary aerosol from local,
combustion-related emissions and that OOA is secondary organic aerosol (SOA)
influenced by regional contributions. There is strong evidence of the direct
correspondence of OOA to SOA during an intense new particle formation and
growth event, when condensational growth of OOA was observed. The fact that
the OOA mass spectrum from this event is very similar to that from the entire
study suggests that the majority of OOA in Pittsburgh is likely SOA. O3
appears to be a poor indicator for OOA concentration while SO42−
is a relatively good surrogate for this dataset. Since the diurnal averages
of HOA track those of CO during day time, oxidation/aging of HOA appears to
be very small on the time scale of several hours. Based on extracted mass
spectra and the likely elemental compositions of major m/z's, the organic mass
to organic carbon ratios (OM:OC) of HOA and OOA are estimated at 1.2 and 2.2 μg/μgC,
respectively, leading to an average OM:OC ratio of 1.8 for
submicron OA in Pittsburgh during September. The C:O ratio of OOA is
estimated at 1:0.8. The carbon contents in HOA and OOA estimated accordingly
correlate well to primary and secondary organic carbon, respectively,
estimated by the OC/EC tracer technique (assuming POC-to-EC ratio=1). In
addition, the total carbon concentrations estimated from the AMS data agree
well with those measured by the Sunset Laboratory Carbon analyzer (r2=0.87; slope=1.01±0.11). Our results represent the first direct
estimate of the OM:OC ratio from highly time-resolved chemical composition
measurements. |
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