Thanks Sergey for your quick response. You are correct, the tool cannot be tested for every type of scenario, and you need users like us to tell you what combination does not work.
Earlier I raised the issue of DDM producing all zero sensitivities, but couldn’t get resolved ( CMAQ-DDM Sensinput Reaction Rates - CMAQ-DDM-3D - CMAS CENTER FORUM). On the PM accuracy, it was pointed to me by a colleague, I will get more information on that.