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| Titel |
Modeling ultrafine particle growth at a pine forest site influenced by anthropogenic pollution during BEACHON-RoMBAS 2011 |
| VerfasserIn |
Y. Y. Cui, A. Hodzic, J. N. Smith, J. Ortega, J. Brioude, H. Matsui, E. J. T. Levin, A. Turnipseed, P. Winkler, B. de Foy |
| 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. 20 ; Nr. 14, no. 20 (2014-10-20), S.11011-11029 |
| Datensatznummer |
250119109
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| Publikation (Nr.) |
 copernicus.org/acp-14-11011-2014.pdf |
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| Zusammenfassung |
| Formation and growth of ultrafine particles is crudely represented
in chemistry-climate models, contributing to uncertainties in aerosol
composition, size distribution, and aerosol effects on cloud condensation
nuclei (CCN) concentrations. Measurements of ultrafine particles, their
precursor gases, and meteorological parameters were performed in a ponderosa
pine forest in the Colorado Front Range in July–August 2011, and were
analyzed to study processes leading to small particle burst events (PBEs)
which were characterized by an increase in the number concentrations of
ultrafine 4–30 nm diameter size particles. These measurements suggest that
PBEs were associated with the arrival at the site of anthropogenic pollution
plumes midday to early afternoon. During PBEs, number concentrations of
4–30 nm diameter particles typically exceeded 104 cm−3, and these
elevated concentrations coincided with increased SO2 and monoterpene
concentrations, and led to a factor-of-2 increase in CCN concentrations at
0.5% supersaturation. The PBEs were simulated using the regional WRF-Chem
model, which was extended to account for ultrafine particle sizes starting
at 1 nm in diameter, to include an empirical activation nucleation scheme in
the planetary boundary layer, and to explicitly simulate the subsequent
growth of Aitken particles (10–100 nm) by condensation of organic and
inorganic vapors. The updated model reasonably captured measured aerosol
number concentrations and size distribution during PBEs, as well as ground-level CCN concentrations. Model results suggest that sulfuric acid
originating from anthropogenic SO2 triggered PBEs, and that the
condensation of monoterpene oxidation products onto freshly nucleated
particles contributes to their growth. The simulated growth rate of
~ 3.4 nm h−1 for 4–40 nm diameter particles was
comparable to the measured average value of 2.3 nm h−1. Results also
suggest that the presence of PBEs tends to modify the composition of sub-20 nm diameter particles, leading to a higher mass fraction of sulfate
aerosols. Sensitivity simulations suggest that the representation of
nucleation processes in the model largely influences the predicted number
concentrations and thus CCN concentrations. We estimate that nucleation
contributes 67% of surface CCN at 0.5% supersaturation in this pine
forest environment. |
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