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| Titel |
Modeling particle nucleation and growth over northern California during the 2010 CARES campaign |
| VerfasserIn |
A. Lupascu, R. Easter, R. Zaveri, M. Shrivastava, M. Pekour, J. Tomlinson, Q. Yang, H. Matsui, A. Hodzic, Q. Zhang, J. D. Fast |
| 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. 21 ; Nr. 15, no. 21 (2015-11-06), S.12283-12313 |
| Datensatznummer |
250120143
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| Publikation (Nr.) |
 copernicus.org/acp-15-12283-2015.pdf |
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| Zusammenfassung |
Accurate representation of the aerosol lifecycle requires adequate modeling
of the particle number concentration and size distribution in addition to
their mass, which is often the focus of aerosol modeling studies. This paper
compares particle number concentrations and size distributions as predicted
by three empirical nucleation parameterizations in the Weather Research and
Forecast coupled with chemistry (WRF-Chem) regional model using 20 discrete
size bins ranging from 1 nm to 10 μm. Two of the parameterizations
are based on H2SO4, while one is based on both H2SO4 and
organic vapors. Budget diagnostic terms for transport, dry deposition,
emissions, condensational growth, nucleation, and coagulation of aerosol
particles have been added to the model and are used to analyze the
differences in how the new particle formation parameterizations influence the
evolving aerosol size distribution. The simulations are evaluated using
measurements collected at surface sites and from a research aircraft during
the Carbonaceous Aerosol and Radiative Effects Study (CARES) conducted in the
vicinity of Sacramento, California.
While all three parameterizations captured the temporal variation of the size
distribution during observed nucleation events as well as the spatial
variability in aerosol number, all overestimated by up to a factor of 2.5 the
total particle number concentration for particle diameters greater than
10 nm. Using the budget diagnostic terms, we demonstrate that the combined
H2SO4 and low-volatility organic vapor parameterization leads to
a different diurnal variability of new particle formation and growth to
larger sizes compared to the parameterizations based on only H2SO4.
At the CARES urban ground site, peak nucleation rates are predicted to occur
around 12:00 Pacific (local) standard time (PST) for the H2SO4
parameterizations, whereas the highest rates were predicted at 08:00 and
16:00 PST when low-volatility organic gases are included in the
parameterization. This can be explained by higher anthropogenic emissions of
organic vapors at these times as well as lower boundary-layer heights that
reduce vertical mixing. The higher nucleation rates in the
H2SO4-organic parameterization at these times were largely offset
by losses due to coagulation. Despite the different budget terms for
ultrafine particles, the 10–40 nm diameter particle number concentrations
from all three parameterizations increased from 10:00 to 14:00 PST and then
decreased later in the afternoon, consistent with changes in the observed
size and number distribution. We found that newly formed particles could
explain up to 20–30 % of predicted cloud condensation nuclei at
0.5 % supersaturation, depending on location and the specific nucleation
parameterization. A sensitivity simulation using 12 discrete size bins
ranging from 1 nm to 10 μm diameter gave a reasonable estimate of
particle number and size distribution compared to the 20 size bin simulation,
while reducing the associated computational cost by ~ 36 %. |
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