Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Environment Color
ENVIRONMENT_AMBIENT
Parameter: Environment Strength
ENVIRONMENT_AMBIENTSTRENGTH
Parameter: Enable Fog
ENVIRONMENT_FOGENABLE
Parameter: Fog Color
ENVIRONMENT_FOG
Parameter: Fog Strength
ENVIRONMENT_FOGSTRENGTH
Parameter: Fog Distance
ENVIRONMENT_FOGDISTANCE
Parameter: Affect Background
ENVIRONMENT_AFFECTBACKGROUND