Aerosol dry deposition on vegetative canopies. Part II: A new modelling approach and applications

This paper presents a new approach for the modelling of aerosol dry deposition on vegetation. It follows a companion article, in which a review of the current knowledge highlights the need for a better description of the aerosol behaviour within the canopy [Petroff, A., Mailliat, A., Amielh, M., Anselmet, F., 2008. Aerosol dry deposition on vegetative canopies. Part I: Review of present knowledge. Atmospheric Environment, in press, http://dx.doi.org/10.1016/j.atmosenv.2007.09.043]. Concepts from multi-phase flow studies are used for describing the canopy medium and deriving a time and space-averaged aerosol balance equation and the associated deposition terms. The closure of the deposition terms follows an up-scaling procedure based on the statistical distribution of the collecting elements. This aerosol transport model is then applied in a stationary and mono-dimensional configuration and takes into account the properties of the vegetation, the aerosol and the turbulent flow. Deposition mechanisms are Brownian diffusion, interception, inertial and turbulent impactions, and gravitational settling. For each of them, a parameterisation of the particle collection is derived and the quality of their predictions is assessed by comparison with wind-tunnel deposition measurements on coniferous twigs [Belot, Y., Gauthier, D., 1975. Transport of micronic particles from atmosphere to foliar surfaces. In: De Vries, D.A., Afgan, N.H. (Eds.), Heat and Mass Transfer in the Biosphere. Scripta Book, Washington, DC, pp. 583–591; Belot, Y., 1977. Etude de la captation des polluants atmosphériques par les végétaux. CEA, R-4786, Fontenay-aux-Roses; Belot, Y., Camus, H., Gauthier, D., Caput, C., 1994. Uptake of small particles by canopies. The Science of the Total Environment 157, 1–6]. Under a real canopy configuration, the predictions of the aerosol transport model compare reasonably well with detailed on-site deposition measurements of Aitken mode particles [Buzorius, G., Rannik, Ü., Mäkelä, J.M., Vesala, T., Kulmala, M., 2000. Vertical aerosol fluxes measured by eddy covariance methods and deposition of nucleation mode particles above a Scots pine forest in southern Finland. Journal of Geophysical Research 105, 19905–19916] and fog droplets [Beswick, K.M., Hargreaves, K.L., Gallagher, M.W., Choularton, T.W., Fowler, D., 1991. Size-resolved measurements of cloud droplet deposition velocity to a canopy using an eddy correlation technique. Quarterly Journal of the Royal Meteorological Society 117, 623–645] on coniferous forest, as well as with a broader data collection both on coniferous forest and grass. Finally, a sensitivity analysis emphasises the main parameters of deposition, which are specific of particle size.