The simultaneous effects of image force and diffusion on ultrafine particle deposition onto vegetation: A wind tunnel study

Figures & data

Figure 1. A sketch of the wind tunnel experimental setup. Illustration of the experimental setup showing the vegetated section inside the wind tunnel, the particle generation inside the mixing chamber and the location of the meshes to homogenize the inflow velocity. The neutralizer and the SMPS unit used to measure concentrations are also shown. The air flow direction is from left to right.

Figure 2. Left panel is a single juniper branch. Right panel is a picture illustration of the juniper branches positioned in the wind tunnel.

Table 1. Percentage of the singly, doubly, and triply charged particle at different sizes (25, 50, 75, and 100 nm) from TDMA results.

	25 nm	50 nm	75 nm	100 nm
+1	97.7 %	94.7%	93.3 %	92.9 %
+2	2.2 %	5.2 %	6.6 %	7 %
+3	<1 %	<1 %	<1 %	<1 %

Figure 3. Penetration values as a function of UFP diameter $d_p$ with (blue) and without (red) the neutralizer in the wind tunnel for different mean wind speeds U_o.

Figure 4. The comparison between measured and fitted penetration values for zero charged (top row) and singly charged (bottom row) particles as a function of UFP diameter.

Figure 5. The coefficient $\beta$ as a function of K_IM for different studies. Note the increase in $\beta$ with declining K_IM.

Figure 6. The relation between single fiber efficiency of image force (E_IM) and the dimensionless number (K_IM) for the 3 wind speed conditions.

Table 2. Comparison of the image force in single fiber theory from different studies.

EIM = β×$\sqrt{K_{IM}}$	KIM	Particle size	Filter type	References
EIM = 1.5×$\sqrt{K_{IM}}$	10^−6 ∼ 10^−2	0.1 and 1 μm	Felt, urethane, and special glass	Lundgren and Whitby (1965)
EIM = 2.3×$\sqrt{K_{IM}}$	10^−6 ∼ 10^−3	1 μm	Glass fiber	Yoshioka, Emi, and Tamori (1968)
EIM = 9.7×$\sqrt{K_{IM}}$ EIM = 29.7×KIM^0.59	10^−7 ∼ 10^−5	25–65 nm	Aluminum and Stainless steel Wire screen	Alonso et al. (2007)
EIM = 24.5×$\sqrt{K_{IM}}$	10^−10 ∼ 10^−8	12.6–102 nm	Vegetation	This study

Figure 7. Scatter plot of the modeled and measured penetration for zero and singly charged particles. The solid line is the 1:1 relation and the dotted line is 20% deviance from the solid line.

Table 3. The goodness of fit values (R² and RMSPE) between model and measurements for zero charged and singly charged particles.

Wind Speed (m/s)	Zero charged		Singly charged
	R^2	RMSPE	R^2	RMSPE
0.3	0.95	9.01%	0.98	66.43%
0.6	0.54	28.07%	0.99	12.83%
0.9	0.87	13.02%	0.90	25.42%

Lundgren, D. A., and K. T. Whitby. 1965. Effect of particle electrostatic charge on filtration by fibrous filters. Ind. Eng. Chem. Process Des. Develop. 4 :345. doi:10.1021/i260016a001.

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Yoshioka, N., H. Emi, and I. Tamori. 1968. Effect of electrostatic force in the filtration efficiency of aerosol. Kagaku Kogaku 32:815–820. doi:10.1252/kakoronbunshu1953.32.815.

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Alonso, M., F. J. Alguacil, J. P. Santos, N. Jidenko, and J. P. Borra. 2007. Deposition of ultrafine aerosol particles on wire screens by simultaneous diffusion and image force. J. Aerosol Sci. 38 (12):1230–1239. doi:10.1016/j.jaerosci.2007.09.004.

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