An apparatus for rotary dumping of rail cars, including a material receiving pit. A rotational frame is disposed at least partially in the pit, is configured to dump a load from a rail car during rotational motion. A backside airflow diverter is disposed within the pit along with a backside hood for removing contaminated air. At least one baffle contacts the upper surface of the backside airflow diverter during at least a portion of the rotational motion. The invention includes an end of hood close off panel extending substantially from a platen supporting wall to the backside air flow diverter or an end ring baffle that extends from a grizzly upwardly to approximately the perimeter of a supporting ring and from the backside airflow diverter toward a dump side of the pit whereby dust laden air is substantially prevented from escaping from the pit under the end ring baffle.