Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Type
OP_PARTICLEDRAW_TYPEParameter: Radius
OP_PARTICLEDRAW_RADIUSParameter: Count
OP_PARTICLEDRAW_COUNTParameter: Draw Position
OP_PARTICLEDRAW_DRAWPOSParameter: Life Time
OP_PARTICLEDRAW_LIFEParameter: Life Variation
OP_PARTICLEDRAW_LIFEVARParameter: Random Seed
OP_PARTICLEDRAW_SEEDParameter: Remove
OP_PARTICLEDRAW_REMOVEParameter: On
OP_PARTICLEDRAW_ONParameter: Animation Time
OP_PARTICLEDRAW_ATIMEParameter: Birth Count
OP_PARTICLEDRAW_OUT_PARTICLECOUNTParameter: Birth Num
OP_PARTICLEDRAW_OUT_PARTICLENUM