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| Titel |
Technical Note: Application of positive matrix factor analysis in heterogeneous kinetics studies utilizing the mixed-phase relative rates technique |
| VerfasserIn |
Y. Liu, S.-M. Li, J. Liggio |
| 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. 17 ; Nr. 14, no. 17 (2014-09-08), S.9201-9211 |
| Datensatznummer |
250119009
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| Publikation (Nr.) |
 copernicus.org/acp-14-9201-2014.pdf |
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| Zusammenfassung |
| The mixed-phase relative rates approach for determining aerosol particle
organic heterogeneous reaction kinetics is often performed utilizing mass
spectral tracers as a proxy for particle-phase reactant concentration.
However, this approach may be influenced by signal contamination
from oxidation products during the experiment. In the current study, the
mixed-phase relative rates technique has been improved by combining a
positive matrix factor (PMF) analysis with electron ionization aerosol mass
spectrometry (unit-mass resolution), thereby removing the influence of m / z
fragments from reaction products on the reactant signals. To demonstrate the
advantages of this approach, the heterogeneous reaction between OH radicals
and citric acid (CA) was investigated using a photochemical flow tube
coupled to a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS).
The measured heterogeneous rate constant (k2) of citric acid toward OH
was
(3.31 ± 0.29) × 10−12 cm3 molecule−1 s−1
at 298 K and (30 ± 3)% relative humidity (RH) and was several times greater
than the results utilizing individual m / z fragments. This phenomenon was
further evaluated for particulate-phase organophosphates (triphenyl phosphate (TPhP), tris-1,3-dichloro-2-propyl phosphate (TDCPP) and tris-2-ethylhexyl phosphate
(TEHP)), leading to k2 values significantly larger than previously
reported. The results suggest that heterogeneous kinetics can be
significantly underestimated when the structure of the products is highly
similar to the reactant and when a non-molecular tracer is measured with a
unit-mass resolution aerosol mass spectrometer. The results also suggest
that the heterogeneous lifetime of organic aerosol in models can be
overestimated due to underestimated OH uptake coefficients. Finally, a
comparison of reported rate constants implies that the heterogeneous
oxidation of aerosols will be dependent upon a number of factors related to
the reaction system, and that a single rate constant for one system cannot
be universally applied under all conditions. |
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