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| Titel |
Development of a new semi-empirical parameterization for below-cloud scavenging of size-resolved aerosol particles by both rain and snow |
| VerfasserIn |
X. Wang, L. Zhang, M. D. Moran |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 7, no. 3 ; Nr. 7, no. 3 (2014-05-12), S.799-819 |
| Datensatznummer |
250115616
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| Publikation (Nr.) |
 copernicus.org/gmd-7-799-2014.pdf |
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| Zusammenfassung |
| A parameter called the scavenging coefficient Λ is widely used in
aerosol chemical transport models (CTMs) to describe below-cloud scavenging
of aerosol particles by rain and snow. However, uncertainties associated with
available size-resolved theoretical formulations for Λ span one to
two orders of magnitude for rain scavenging and nearly three orders of
magnitude for snow scavenging. Two recent reviews of below-cloud scavenging
of size-resolved particles recommended that the upper range of the available
theoretical formulations for Λ should be used in CTMs based on
uncertainty analyses and comparison with limited field experiments. Following
this recommended approach, a new semi-empirical parameterization for
size-resolved Λ has been developed for below-cloud scavenging of
atmospheric aerosol particles by both rain (Λrain) and snow
(Λsnow). The new parameterization is based on the 90th
percentile of Λ values from an ensemble data set calculated using
all possible "realizations" of available theoretical Λ formulas
and covering a large range of aerosol particle sizes and precipitation
intensities (R). For any aerosol particle size of diameter d, a strong
linear relationship between the 90th-percentile log10 (Λ) and
log10 (R), which is equivalent to a power-law relationship between
Λ and R, is identified. The log-linear relationship, which is
characterized by two parameters (slope and y intercept), is then further
parameterized by fitting these two parameters as polynomial functions of
aerosol size d. A comparison of the new parameterization with limited
measurements in the literature in terms of the magnitude of Λ and
the relative magnitudes of Λrain and
Λsnow suggests that it is a reasonable approximation.
Advantages of this new semi-empirical parameterization compared to
traditional theoretical formulations for Λ include its applicability
to below-cloud scavenging by both rain and snow over a wide range of particle
sizes and precipitation intensities, ease of implementation in any CTM with a
representation of size-distributed particulate matter, and a known
representativeness, based on the consideration in its development, of all
available theoretical formulations and field-derived estimates for Λ
(d) and their associated uncertainties. |
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