The difference of vertical advection and convection process for chemistry species

Question

In atmospheric, the change of mixing ration $C_i$ of a chemical species $i$ is determined by:

$\frac{\partial C_i }{\partial t} = -\bigtriangledown (VC_i)+\frac{\partial }{\partial z}(k_z\frac{\partial C_i }{\partial z}) + (\frac{\partial C_i }{\partial z})_{dry}++ (\frac{\partial C_i }{\partial z})_{wet}+(\frac{\partial C_i }{\partial z})_{conv}+P_i-L_i+E_i$

1. The first term represent the $Ci$ change due to horizontal and vertical advection.
2. 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

Answer 1

The difference between advection and convection in Chemistry Transport models (CTMs) is a question of scale:

• Advection is driven by winds that are provided by the meteorological input dataset. Thus, the wind is resolved in the meteorological data.
• Convection is driven by sub grid processes (e.g. temperature gradients) and is paramterized in CTMs.

See for example:

• Pleim, 2007a. doi: 10.1175/JAM2539.1
• Pleim, 2007b. doi: 10.1175/JAM2534.1
• Rasch et al., 1997. doi: 10.1029/97JD02087