Development of a parameterization scheme for calculating dry deposition velocity of fine, coarse and giant particles

Abstract

Abstract. A parameterization scheme is developed for calculating bulk dry deposition velocity (Vd) of fine (PM2.5-particles having a diameter of ≤ 2.5 μm), coarse (PM2.5–10-particles having a diameter of 2.5–10 μm), and giant (PM10+-particles having a diameter of > 10 μm) atmospheric particles. The parameterization scheme is developed from an empirical fit of Vd data calculated using the size-resolved Vd scheme of Zhang et~al. (2001) with assumed lognormal size distributions of PM2.5, PM2.5–10 and PM10+. In the new scheme, the surface deposition velocity (Vds) is parameterized as a simple linear function of friction velocity (u*) for PM2.5 and as a polynomial function of u* for both PM2.5–10 and PM10+ over all the 26 land use categories (LUCs). An adjustment factor as an exponential function of u* and leaf area index (LAI) is also applied to Vds of PM2.5–10 and PM10+ over nine of the 26 LUCs that have variable LAI. Constant gravitational settling velocities are provided for PM2.5, PM2.5–10 and PM10+. Aerodynamic resistance between a reference height and the surface can be calculated using available analytical formulas from literature. The bulk Vd of PM2.5, PM2.5–10 and PM10+ at the reference height can then be calculated by combining the gravitational settling velocity, aerodynamic resistance and the parameterized Vds. The new parameterization scheme agrees reasonably well with the original size-resolved scheme and provides an alternative approach for calculating Vd of fine, coarse and giant particles. Vd of any particle species can be simply estimated using this scheme as long as the mass fraction in fine, coarse and giant particles are known or can be assumed.