Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Position
OUT_PART_POSITION
Parameter: Velocity
OUT_PART_VELOCITY
Parameter: Age
OUT_PART_AGE
Parameter: Life
OUT_PART_LIFE
Parameter: Size
OUT_PART_SIZE
Parameter: Scale
OUT_PART_SCALE
Parameter: Mass
OUT_PART_MASS
Parameter: Alignment
OUT_PART_ALIGNMENT
Parameter: DT Factor
OUT_PART_DTFAC
Parameter: Random Seed
OUT_PART_RANDOMSEED
Parameter: Color
OUT_PART_COLOR