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| Titel |
Characterization of a real-time tracer for isoprene epoxydiols-derived secondary organic aerosol (IEPOX-SOA) from aerosol mass spectrometer measurements |
| VerfasserIn |
W. W. Hu, P. Campuzano-Jost, B. B. Palm, D. A. Day, A. M. Ortega, P. L. Hayes, J. E. Krechmer, Q. Chen, M. Kuwata, Y. J. Liu, S. S. Sá, K. McKinney, S. T. Martin, M. Hu, S. H. Budisulistiorini, M. Riva, J. D. Surratt, J. M. Clair, G. Isaacman-Van Wertz, L. D. Yee, A. H. Goldstein, S. Carbone, J. Brito, P. Artaxo, J. A. Gouw, A. Koss, A. Wisthaler, T. Mikoviny, T. Karl, L. Kaser, W. Jud, A. Hansel, K. S. Docherty, M. L. Alexander, N. H. Robinson, H. Coe, J. D. Allan, M. R. Canagaratna, F. Paulot, 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 ; 15, no. 20 ; Nr. 15, no. 20 (2015-10-23), S.11807-11833 |
| Datensatznummer |
250120118
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| Publikation (Nr.) |
 copernicus.org/acp-15-11807-2015.pdf |
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| Zusammenfassung |
| Substantial amounts of secondary organic aerosol (SOA) can be formed from
isoprene epoxydiols (IEPOX), which are oxidation products of isoprene mainly
under low-NO conditions. Total IEPOX-SOA, which may include SOA formed from
other parallel isoprene oxidation pathways, was quantified by applying
positive matrix factorization (PMF) to aerosol mass spectrometer (AMS)
measurements. The IEPOX-SOA fractions of organic aerosol (OA) in multiple field studies across
several continents are summarized here and show consistent patterns with the
concentration of gas-phase IEPOX simulated by the GEOS-Chem chemical
transport model. During the Southern Oxidant and Aerosol Study (SOAS),
78 % of PMF-resolved IEPOX-SOA is accounted by the measured IEPOX-SOA
molecular tracers (2-methyltetrols, C5-Triols, and IEPOX-derived organosulfate
and its dimers), making it the highest level of molecular identification of
an ambient SOA component to our knowledge. An enhanced signal at
C5H6O+ (m/z 82) is found in PMF-resolved IEPOX-SOA spectra.
To investigate the suitability of this ion as a tracer for IEPOX-SOA, we
examine fC5H6O
(fC5H6O=
C5H6O+/OA) across multiple field,
chamber, and source data sets. A background of
~ 1.7 ± 0.1 ‰ (‰ = parts per thousand) is
observed in studies strongly influenced by urban, biomass-burning, and other
anthropogenic primary organic aerosol (POA). Higher background values of
3.1 ± 0.6 ‰ are found in studies strongly influenced by
monoterpene emissions. The average laboratory monoterpene SOA value
(5.5 ± 2.0 ‰) is 4 times lower than the average for IEPOX-SOA
(22 ± 7 ‰), which leaves some room to separate both
contributions to OA. Locations strongly influenced by isoprene emissions
under low-NO levels had higher fC5H6O
(~ 6.5 ± 2.2 ‰ on average) than other sites, consistent
with the expected IEPOX-SOA formation in those studies.
fC5H6O in IEPOX-SOA is always elevated
(12–40 ‰) but varies substantially between locations, which is
shown to reflect large variations in its detailed molecular composition. The
low fC5H6O (< 3 ‰) reported in
non-IEPOX-derived isoprene-SOA from chamber studies indicates that this
tracer ion is specifically enhanced from IEPOX-SOA, and is not a tracer for
all SOA from isoprene. We introduce a graphical diagnostic to study the
presence and aging of IEPOX-SOA as a triangle plot of fCO2
vs. fC5H6O. Finally, we develop a simplified
method to estimate ambient IEPOX-SOA mass concentrations, which is shown to
perform well compared to the full PMF method. The uncertainty of the tracer
method is up to a factor of ~ 2, if the
fC5H6O of the local IEPOX-SOA is not
available. When only unit mass-resolution data are available, as with the
aerosol chemical speciation monitor (ACSM), all methods may perform less well
because of increased interferences from other ions at m/z 82. This study
clarifies the strengths and limitations of the different AMS methods for
detection of IEPOX-SOA and will enable improved characterization of this OA
component. |
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