Dry deposition profile of small particles within a model spruce canopy

Data on dry deposition of 0.82 mum MMAD uranium particles to a small scale. 'model' Norway spruce (Picea abies) canopy have been determined by means of wind tunnel experiments. These are presented for both the total canopy and for five horizontal layers within the canopy. The results show a complex pattern of deposition within the canopy. The highest deposition velocity V(g) (0.19 cm s(-1)) was recorded for the topmost layer within the canopy (i.e. the layer in direct contact with the boundary layer) whereas the lowest V(g) (0.02 cm s(-1)) occurred at the soil surface. Vertical penetration of depositing aerosol through the canopy was influenced by variations in biomass, wind velocity and turbulence within the canopy. A total canopy V(g) of 0.5 cm s(-1) was obtained and this is in line with field measurements of V(g) reported in literature for both anthropogenic and radionuclide aerosols of similar size ranges. Extrapolation of wind tunnel data to 'real' forest canopies is discussed. The information presented here is of importance in predicting the likely contribution of dry deposition of aerosols to pollutant inputs to forest ecosystems, particularly in the context of radioactive aerosol releases from nuclear installations. The application of the present data may also be appropriate for other pollutant aerosols such as SO(4), NO(3) and NH(4), which are characterised by particle sizes in the range used in this study. (C) 2002 Elsevier Science B.V. All rights reserved.