Ansys Employee

I'd tend to just use a single value for heat capacity, conductivity and viscosity as they're all gases and more-or-less the same. You also need to consider the mass flow of each pollutant species: do you learn more by adding all 6 species or would you learn the same for less cpu with 2 (emission and air). Note, 3 may be sensible, water vapour, pollutant and air if you want to find out if the plume will be visible. 

What gas density did you set? If the mixture is volume weighted the species each have a (unknown to me) value. 

Check the gravity vector. If z is up, does gravity really have a positive value?