vertical diffusivity

例句：

1. 1. The rate of vertical diffusion is affected by the concentration gradient.
   垂直扩散速率受到浓度梯度的影响。
2. 2. In a chemical reaction, the vertical diffusion coefficient determines the rate of material transfer.
   在化学反应中，垂直扩散系数决定了物质转移的速度。
3. 3.The vertical diffusivity of a gas in a porous medium depends on its molecular size and shape.
   气体在多孔介质中的垂直扩散系数取决于其分子大小和形状。