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| Titel |
Semicontinuous measurements of gas–particle partitioning of organic acids in a ponderosa pine forest using a MOVI-HRToF-CIMS |
| VerfasserIn |
R. L. N. Yatavelli, H. Stärk, S. L. Thompson, J. R. Kimmel, M. J. Cubison, D. A. Day, P. Campuzano-Jost, B. B. Palm, A. Hodzic, J. A. Thornton, J. T. Jayne, D. R. Worsnop, 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 ; 14, no. 3 ; Nr. 14, no. 3 (2014-02-11), S.1527-1546 |
| Datensatznummer |
250118367
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| Publikation (Nr.) |
 copernicus.org/acp-14-1527-2014.pdf |
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| Zusammenfassung |
| Hundreds of gas- and particle-phase organic acids were measured in a rural
ponderosa pine forest in Colorado, USA, during BEACHON-RoMBAS (Bio-hydro-atmosphere
interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen –
Rocky Mountain Biogenic Aerosol Study). A recently developed
micro-orifice volatilization impactor high-resolution time-of-flight
chemical ionization mass spectrometer (MOVI-HRToF-CIMS) using acetate
(CH3C(O)O−) as the reagent ion was used to selectively ionize and
detect acids semicontinuously from 20 to 30 August 2011, with a
measurement time resolution of ~1.5 h. At this site 98%
of the organic acid mass is estimated to be in the gas phase, with only
~2% in the particle phase. We investigated gas–particle
partitioning, quantified as the fraction in the particle phase (Fp), of
C1–C18 alkanoic acids, six known terpenoic acids, and bulk organic
acids vs. carbon number. Data were compared to the absorptive partitioning
model and suggest that bulk organic acids at this site follow absorptive
partitioning to the organic aerosol mass. The rapid response
(<1–2 h) of partitioning to temperature changes for bulk acids suggests that
kinetic limitations to equilibrium are minor, which is in contrast to
conclusions of some recent laboratory and field studies, possibly due to
lack of very low ambient relative humidities at this site. Time trends for
partitioning of individual and groups of acids were mostly captured by the
model, with varying degrees of absolute agreement. Species with predicted
substantial fractions in both the gas and particle phases show better
absolute agreement, while species with very low predicted fractions in one
phase often show poor agreement, potentially due to thermal decomposition,
inlet adsorption, or other issues. Partitioning to the aqueous phase is
predicted to be smaller than to the organic phase for alkanoic and bulk
acids, and has different trends with time and carbon number than observed
experimentally. This is due to the limited additional functionalization
observed for the bulk acids. Partitioning to water appears to only play a
role for the most oxidized acids during periods of high aerosol liquid
water. Based on measurement–model comparison we conclude that species carbon
number and oxygen content, together with ambient temperature, control the
volatility of organic acids and are good predictors for partitioning at this
site. Partitioning of bulk acids is more consistent with model predictions
for hydroxy acids, hydroperoxyacids, or polyacids, and less so for keto acids. |
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