In this paper, a method of calculating lateral turbulent diffusivity K_Y and Lagrangian time scale T_LY by using the parameters in the atmospheric boundary is suggested. Our main hypothesis is that Ky and T_LY are dependent upon the characteristics of the lateral turbulent spectrum σ_v and λ_mv. It is shown by model computation that the simulation results using T_LY presented here are in good agreement with the observational data.