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Scavenging of ultrafine particles by rainfall at a boreal site: observations and model estimations

Andronache, C. ; Gronholm, T. ; Laakso, L. ; Phillips, Vaughan LU and Venalainen, A. (2006) In Atmospheric Chemistry and Physics 6. p.4739-4754
Abstract
Values of the scavenging coefficient determined from observations of ultrafine particles ( with diameters in the range 10 - 510 nm) during rain events at a boreal forest site in Southern Finland between 1996 and 2001 were reported by Laakso et al. (2003a). The estimated range of the median values of the scavenging coefficient was [ 7 x 10(-6)- 4 x 10(-5)] s(-1), which is generally higher than model calculations based only on below-cloud processes (Brownian diffusion, interception, and typical phoretic and charge effects). In the present study, in order to interpret these observed data on scavenging coefficients from Laakso et al. ( 2003a), we use a model that includes below-cloud scavenging processes, mixing of ultrafine particles from the... (More)
Values of the scavenging coefficient determined from observations of ultrafine particles ( with diameters in the range 10 - 510 nm) during rain events at a boreal forest site in Southern Finland between 1996 and 2001 were reported by Laakso et al. (2003a). The estimated range of the median values of the scavenging coefficient was [ 7 x 10(-6)- 4 x 10(-5)] s(-1), which is generally higher than model calculations based only on below-cloud processes (Brownian diffusion, interception, and typical phoretic and charge effects). In the present study, in order to interpret these observed data on scavenging coefficients from Laakso et al. ( 2003a), we use a model that includes below-cloud scavenging processes, mixing of ultrafine particles from the boundary layer (BL) into cloud, followed by cloud condensation nuclei activation and in-cloud removal by rainfall. The range of effective scavenging coefficient predicted by the new model, corresponding to wide ranges of values of its input parameters, are compared with observations. Results show that ultrafine particle removal by rain depends on aerosol size, rainfall intensity, mixing processes between BL and cloud elements, in-cloud scavenged fraction, in-cloud collection efficiency, and in-cloud coagulation with cloud droplets. The scavenging coefficients predicted by the new model are found to be significantly sensitive to the choice of representation of: ( 1) mixing processes; ( 2) raindrop size distribution; ( 3) phoretic effects in aerosol-raindrop collisions; and ( 4) cloud droplet activation. Implications for future studies of BL ultrafine particles scavenging are discussed. (Less)
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author
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published
subject
in
Atmospheric Chemistry and Physics
volume
6
pages
4739 - 4754
publisher
Copernicus Gesellschaft mbH
external identifiers
  • wos:000241541500002
  • scopus:33750284146
ISSN
1680-7324
language
English
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no
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bdf8c80b-7199-48e0-b8eb-eb3ce1bfde46 (old id 4587545)
date added to LUP
2016-04-01 12:18:39
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2020-01-15 02:40:59
@article{bdf8c80b-7199-48e0-b8eb-eb3ce1bfde46,
  abstract     = {Values of the scavenging coefficient determined from observations of ultrafine particles ( with diameters in the range 10 - 510 nm) during rain events at a boreal forest site in Southern Finland between 1996 and 2001 were reported by Laakso et al. (2003a). The estimated range of the median values of the scavenging coefficient was [ 7 x 10(-6)- 4 x 10(-5)] s(-1), which is generally higher than model calculations based only on below-cloud processes (Brownian diffusion, interception, and typical phoretic and charge effects). In the present study, in order to interpret these observed data on scavenging coefficients from Laakso et al. ( 2003a), we use a model that includes below-cloud scavenging processes, mixing of ultrafine particles from the boundary layer (BL) into cloud, followed by cloud condensation nuclei activation and in-cloud removal by rainfall. The range of effective scavenging coefficient predicted by the new model, corresponding to wide ranges of values of its input parameters, are compared with observations. Results show that ultrafine particle removal by rain depends on aerosol size, rainfall intensity, mixing processes between BL and cloud elements, in-cloud scavenged fraction, in-cloud collection efficiency, and in-cloud coagulation with cloud droplets. The scavenging coefficients predicted by the new model are found to be significantly sensitive to the choice of representation of: ( 1) mixing processes; ( 2) raindrop size distribution; ( 3) phoretic effects in aerosol-raindrop collisions; and ( 4) cloud droplet activation. Implications for future studies of BL ultrafine particles scavenging are discussed.},
  author       = {Andronache, C. and Gronholm, T. and Laakso, L. and Phillips, Vaughan and Venalainen, A.},
  issn         = {1680-7324},
  language     = {eng},
  pages        = {4739--4754},
  publisher    = {Copernicus Gesellschaft mbH},
  series       = {Atmospheric Chemistry and Physics},
  title        = {Scavenging of ultrafine particles by rainfall at a boreal site: observations and model estimations},
  volume       = {6},
  year         = {2006},
}