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| Titel |
High-resolution chemical ionization mass spectrometry (ToF-CIMS): application to study SOA composition and processing |
| VerfasserIn |
D. Aljawhary, A. K. Y. Lee, J. P. D. Abbatt |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 11 ; Nr. 6, no. 11 (2013-11-26), S.3211-3224 |
| Datensatznummer |
250085115
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| Publikation (Nr.) |
 copernicus.org/amt-6-3211-2013.pdf |
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| Zusammenfassung |
| This paper demonstrates the capabilities of chemical ionization mass
spectrometry (CIMS) to study secondary organic aerosol (SOA) composition
with a high-resolution (HR) time-of-flight mass analyzer (aerosol-ToF-CIMS).
In particular, by studying aqueous oxidation of water-soluble organic
compounds (WSOC) extracted from α-pinene ozonolysis SOA, we assess
the capabilities of three common CIMS reagent ions: (a) protonated water
clusters (H2O)nH+, (b) acetate CH3C(O)O− and (c)
iodide water clusters I(H2O)n− to monitor SOA composition. Furthermore, we report the relative sensitivity of these reagent ions to a wide
range of common organic aerosol constituents. We find that
(H2O)nH+ is more selective to the detection of less oxidized
species, so that the range of O / C and OSC (carbon oxidation state) in
the SOA spectra is considerably lower than those measured using
CH3C(O)O− and I(H2O)n−. Specifically,
(H2O)nH+ ionizes organic compounds with OSC ≤ 1.3,
whereas CH3C(O)O− and I(H2O)n− both ionize highly
oxygenated organics with OSC up to 4 with I(H2O)n−
being more selective towards multi-functional organic compounds. In the bulk
O / C and H / C space (in a Van Krevelen plot), there is a remarkable
agreement in both absolute magnitude and oxidation trajectory between
ToF-CIMS data and those from a high-resolution aerosol mass spectrometer
(HR-AMS). Despite not using a sensitivity-weighted response for the ToF-CIMS
data, the CIMS approach appears to capture much of the chemical change
occurring. As demonstrated by the calibration experiments with standards,
this is likely because there is not a large variability in sensitivities
from one highly oxygenated species to another, particularly for the
CH3C(O)O− and I(H2O)n− reagent ions. Finally, the
data illustrate the capability of aerosol-ToF-CIMS to monitor specific
chemical change, including the fragmentation and functionalization reactions
that occur during organic oxidation, and the oxidative conversion of dimeric
SOA species into monomers. Overall, aerosol-ToF-CIMS is a valuable,
selective complement to some common SOA characterization methods, such as
AMS and spectroscopic techniques. Both laboratory and ambient SOA samples
can be analyzed using the techniques illustrated in the paper. |
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