Particle deposition to forests: An alternative to K-theory

• Published in: Atmospheric environment (1994) Vol. 94; pp. 593 - 605
• Main Authors: Huang, Cheng-Wei, Launiainen, Samuli, Grönholm, Tiia, Katul, Gabriel G.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.09.2014; Elsevier
• Subjects: Atmospheric aerosol particles; Canopy turbulence; Convection, turbulence, diffusion. Boundary layer structure and dynamics; Earth, ocean, space; Exact sciences and technology; External geophysics; Geophysics. Techniques, methods, instrumentation and models; Meteorology; Particle flux budget; Particles and aerosols; Pinus sylvestris; Second-order closure model; Size-resolved model; Scandinavia; Europe; Finland; ANE, Finland; Canopy turbulence; Size-resolved model; Second-order closure model; Particle flux budget; Atmospheric aerosol particles; Atmospheric fallout; Turbulent diffusion; Modeling; Dry deposition; Closure model; Particle size distribution; Flux density; Atmospheric boundary layer; Aerosol deposition; Canopy(vegetation); Coniferous forest
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2014.05.072

It has been known for some time that flux-gradient closure schemes (or K-theory), widely used to model the aerosol sized particle turbulent diffusivity, are problematic within canopies. Reported momentum transport in a zero- or counter-mean velocity gradient flow within open trunk spaces of forests is prototypical of the failure of K-theory. To circumvent this problem, a multi-layered and size-resolved second-order closure model is developed using the mean particle turbulent flux budget as a primary closure for the particle turbulent flux instead of K-theory. The proposed model is evaluated against the multi-level size-resolved particle fluxes and particle concentration measurements conducted within and above a tall Scots pine forest situated in Hyytiälä, Southern Finland. Conditions promoting the failure of K-theory for different particle sizes and canopy layers and the characteristics of the particle transport processes within the canopy sub-layer (CSL) are discussed. Using the model, it is shown that K-theory may still be plausible for modeling the particle deposition velocity when the particle size range is smaller than 1 μm provided the local particle turbulent diffusivity is estimated from the characteristic turbulent relaxation time scale and the vertical velocity variance. Model calculations suggest that the partitioning of particle deposition onto foliage and forest floor appears insensitive to the friction velocity for particles smaller than 100 nm (ultrafine), but decreases with increasing friction velocity for particles larger than 100 nm (accumulation and coarse modes). •A particle flux budget is proposed as an alternative to K-theory within canopies.•K-theory appears plausible for particle sizes (dp) < 1 μm.•Deposition velocity increases with increasing friction velocity (u∗).•Partitioning of particle deposition between forest floor and canopy explored.•The partitioning is dp dependent for dp < 100 nm and u∗ dependent for dp > 100 nm.