In atmospheric, the change of mixing ration $C_i$ of a chemical species $i$ is determined by:
$\frac{\partial C_i }{\partial t} = -\bigtriangledown (VC_i)+\frac{\partial }{\partial z}(k_z\frac{\partial C_i }{\partial z}) + (\frac{\partial C_i }{\partial z})_{dry}++ (\frac{\partial C_i }{\partial z})_{wet}+(\frac{\partial C_i }{\partial z})_{conv}+P_i-L_i+E_i$
- The first term represent the $Ci$ change due to horizontal and vertical advection.
- The fifith term on the right hand represent the $Ci$ due to the vertical convection.
I have read about this question "What exactly is the difference between advection and convection?".
The answer told, which I quoted:
Advection is the movement of some material dissolved or suspended in the fluid.
Convection is the movement of a fluid, typically in response to heat.
But when we are just talking about the chemical species. They are not in fluid form. So,how dos the convection process mean?
Update: The equation was from a phD dissertatio Climate and Air Pollution Modeling in South America focus on Megacities. Links here