Dry deposition describes the process of aerodynamic transport of a particle to the near-surface viscous sublayer where diffusion, turbulent diffusion and gravitational settling deliver the particle to the surface. Zufall et al. (1998) provide convincing evidence that particle deposition is dominated by large particles even though atmospheric particle size distributions are dominated by particles less than 1 |im mass median diameter (mmd). Therefore, the dry deposition flux is calculated as:
= Vd (0.5 cm s-1) X [SOCpart] (pg m-3) x 864 (unit adjustment) (1)
We selected a value for the Vd of 0.5 cm s-1 reflecting the disproportionate influence that large particles have on atmospheric deposition, especially in urbanized and industrialized regions (see Franz etal., 1998;Zufalletal., 1998;Caffreyetal., 1998). We believe that this maybe an underestimate and studies are underway to better estimate particle size -dependent deposition velocities.
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