This is the vertical cross section of zonal mean from the first timestep to the end of a year.  You can also find that the mixing is occurred within the northern hemisphere.  And about 3 months later, concentration has mixing to the southern hemisphere.  But, the negative concentration is showing up over the top of Southern Pole, which seems to result from the numerical problem of spectral model.  But, we do not want to spend too much time to improve the model itself.  So, we decided to use the current state of model.