三、 The movement of soil air (一)、 Convection( Mass flow) Convection -The soil air is transferred from higher pressure area to lower pressure area. D q -(k nVp Where gv is the volume convective flux of air; k is the permeability of the air-filled pore space; n is the viscosity of soil air; vis the pressure gradient in soil air二、 The movement of soil air （一）、Convection (Mass Flow) Convection –The soil air is transferred from higher pressure area to lower pressure area. Where qv is the volume convective flux of air; k is the permeability of the air-filled pore space; is the viscosity of soil air; is the pressure gradient in soil air. qv = −(k /)p   