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| Titel |
Factors controlling pollutant plume length downwind of major roadways in nocturnal surface inversions |
| VerfasserIn |
W. Choi, A. M. Winer, S. E. Paulson |
| 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. 13 ; Nr. 14, no. 13 (2014-07-04), S.6925-6940 |
| Datensatznummer |
250118871
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| Publikation (Nr.) |
 copernicus.org/acp-14-6925-2014.pdf |
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| Zusammenfassung |
| A fitting method using a semi-empirical Gaussian dispersion model solution
was successfully applied to obtain both dispersion coefficients and a
particle number emission factor (PNEF) directly from ultrafine particle (UFP;
particles smaller than <0.1 μm in diameter) concentration
profiles observed downwind of major roadways in California's South Coast Air
Basin (SoCAB). The effective Briggs' formulation for the vertical dispersion
parameter σz was adopted in this study due to its better
performance in describing the observed profiles compared to other
formulations examined. The two dispersion coefficients in Briggs'
formulation, α and β, ranged from 0.02 to 0.07 and from
−0.5 × 10−3 to 2.8 × 10−3, respectively, for
the four freeway transects studied and are significantly different for
freeways passing over vs. under the street on which measurements of the
freeway plume were made. These ranges are wider than literature values for
α and β under stable conditions. The dispersion coefficients
derived from observations showed strong correlations with both surface
meteorology (wind speed/direction, temperature, and air stability) and
differences in concentrations between the background and plume peak. The
relationships were applied to predict freeway plume transport using a
multivariate regression, and produced excellent agreement with observed UFP
concentration profiles. The mean PNEF for a mixed vehicle fleet on the four
freeways was estimated as
7.5 × 1013 particles km−1 vehicle−1, which is
about 15% of the value estimated in 2001 for the I-405 freeway, implying
significant reductions in UFP emissions over the past decade in the SoCAB. |
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