Contribution To Reducing Uncertainties
Regarding The Dry Deposition Velocities Of
Fine Aerosols: Study Case Of A Prairie
(description Of Experimental Methods
And Comparison With Models)
Author(s)
O. Connan, D. Maro, D. Hébert, M. Rozet, B. Checiak & L. Solier
Abstract
In the context of environmental protection, the transfer of aerosols to vegetative
canopies must be properly estimated, since aerosols constitute a preferential
transport pathway for atmospheric pollution (bacteriological, chemical or
radioactive). In order to properly assess the transport of pollutants, it is essential
to accurately determine their dry deposition fluxes. Previous studies conducted
around a nuclear site showed that the deposition prediction models do not yield
an accurate representation of measured radionuclide activity (mainly 106Ru) in
grasses, with observed discrepancies probably attributable to an underestimate of
the dry deposition velocities. In addition, the literature mentions uncertainties in
the order of two decades for the deposition velocities of particles larger than 1
µm, and little experimental data is available for submicronic particles. In order to
reduce these uncertainties and choose a suitable model, a series of experiments to
measure the dry deposition velocities of aerosols has been scheduled for 2005-
2007. This document presents the method used and the results obtained for a fine
aerosol (0.24 µm) dispersed over a prairie under neutral or unstable
meteorological conditions. The technique used consists of generating a
monodispersed fluorescein aerosol. The fluorescein concentration is measured in
the grass and air by spectrofluorimetry and used to obtain the dry deposition
velocities. A second approach using natural radioactivity (214Pb) and gamma
spectrophotometry measurements has enabled the confirmation of the results
obtained. The mean deposition velocities measured in this first series of
experiments for a prairie-type substrate vary between 4 10-4 and 2 10-3 m.s-1.
The comparison with the Slinn, Zhang and Wesely models shows that the first of
these underestimates the deposition velocities by a factor of 5 to 20 and the other
two more accurately represent the experimental measurements, with
model/measurement discrepancies of generally less than 2.
Keywords: deposition velocity, contaminant aerosol.
Keywords
deposition velocity, contaminant aerosol.
Related Book
Other papers in this volume
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