Direct numerical simulations were carried out to investigate the differential thermal and mass diffusions in canonical free turbulent shear flows,i.e.,turbulent mixing layer and homogeneous isotropic turbulence.This research is a part of the project to determine the Lewis number effect on the aerosol nucleation rate in turbulent flows.The numerical code adopts finite difference scheme on structured grid,which was developed at Standford University and adapted by the authors for the current research.The simulations were performed on a 64 cores workstation in parallel.