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| Titel |
Development of a source oriented version of the WRF/Chem model and its application to the California regional PM10 / PM2.5 air quality study |
| VerfasserIn |
H. Zhang, S. P. DeNero, D. K. Joe, H.-H. Lee, S.-H. Chen, J. Michalakes, M. J. Kleeman |
| 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. 1 ; Nr. 14, no. 1 (2014-01-15), S.485-503 |
| Datensatznummer |
250118265
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| Publikation (Nr.) |
 copernicus.org/acp-14-485-2014.pdf |
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| Zusammenfassung |
A source-oriented version of the Weather Research and Forecasting model with chemistry (SOWC,
hereinafter) was developed. SOWC separately tracks primary particles with different hygroscopic
properties rather than instantaneously combining them into an internal mixture. This approach
avoids artificially mixing light absorbing black + brown carbon particles with materials such as
sulfate that would encourage the formation of additional coatings. Source-oriented particles
undergo coagulation and gas-particle conversion, but these processes are considered in a dynamic
framework that realistically "ages" primary particles over hours and days in the
atmosphere. SOWC more realistically predicts radiative feedbacks from anthropogenic aerosols
compared to models that make internal mixing or other artificial mixing assumptions.
A three-week stagnation episode (15 December 2000 to 6 January 2001) in the San Joaquin Valley
(SJV) during the California Regional PM10 / PM2.5 Air Quality Study (CRPAQS)
was chosen for the initial application of the new modeling system. Primary particles emitted from
diesel engines, wood smoke, high-sulfur fuel combustion, food cooking, and other anthropogenic
sources were tracked separately throughout the simulation as they aged in the atmosphere.
Differences were identified between predictions from the source oriented vs. the internally mixed
representation of particles with meteorological feedbacks in WRF/Chem for a number of
meteorological parameters: aerosol extinction coefficients, downward shortwave flux, planetary
boundary layer depth, and primary and secondary particulate matter concentrations. Comparisons with
observations show that SOWC predicts particle scattering coefficients more accurately than the
internally mixed model. Downward shortwave radiation predicted by SOWC is enhanced by
~1% at ground level chiefly because diesel engine particles in the source-oriented mixture
are not artificially coated with material that increases their absorption efficiency. The
extinction coefficient predicted by SOWC is reduced by an average of 0.012 km−1
(4.8%) in the SJV with a maximum reduction of ~0.2 km−1. Planetary boundary
layer (PBL) height is increased by an average of 5.2 m (1.5%) with a~maximum of ~100 m
in the SJV. Particulate matter concentrations predicted by SOWC are
2.23 μg m−3 (3.8%) lower than the average by the internally mixed version of the
same model in the SJV because increased solar radiation at the ground increases atmospheric
mixing.
The changes in predicted meteorological parameters and particle concentrations identified in the
current study stem from the mixing state of black carbon. The source-oriented model representation
with realistic aging processes predicts that hydrophobic diesel engine particles remain largely
uncoated over the +7 day simulation period, while the internal mixture model representation
predicts significant accumulation of secondary nitrate and water on diesel engine
particles. Similar results will likely be found in any air pollution stagnation episode that is
characterized by significant particulate nitrate production. Future work should consider episodes
where coatings are predominantly sulfate and/or secondary organic aerosol. |
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