DPM Concentration: Mass-average or Area-average
 

When computing the DPM Concentration over a plane, there are two options - mass-averaged or area-averaged. I tried with both, and the values at up to 50% difference. I think area-averaged would be the correct one to use and would like to seek any thoughts on this.

By the way, when computing the standard deviation of the DPM concentration on the same plane, there is not a mass-averaged versus area-averaged option.
Should I try doing so by hand in a spreadsheet, or, the non-weighted value given by Fluent is accurate enough?

Thanks.