# 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:

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

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.

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

• Conv = Convective Precipitation? Wet could only mean non-convective precipitation. Mar 29, 2016 at 8:33
• Could you give a reference to the equation? Mar 29, 2016 at 8:44
• why aren't the chemical species in fluid form? aren't they subject to the same movement?
– f.thorpe
Mar 30, 2016 at 23:06
• @farrenthorpe. In my opinion, chemical in particular phase were also included. Mar 31, 2016 at 5:21