Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Environment Color
ENVIRONMENT_AMBIENTParameter: Environment Strength
ENVIRONMENT_AMBIENTSTRENGTHParameter: Enable Fog
ENVIRONMENT_FOGENABLEParameter: Fog Color
ENVIRONMENT_FOGParameter: Fog Strength
ENVIRONMENT_FOGSTRENGTHParameter: Fog Distance
ENVIRONMENT_FOGDISTANCEParameter: Affect Background
ENVIRONMENT_AFFECTBACKGROUND