The difference of vertical advection and convection process for chemistry species 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
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