You could bandclamp a ventilated hood over it provided you don't restrict the air volume.  But keep this in mind, during the winter months off gassing and ventilation is releasing moist and warmer than outside air that will condense and possibly freeze up and build ice reducing the air flow. Consider a electric heat tape if needed. 

put a cap on it...you can get one at lowes or home depot..they can be galvanized or plastic..doesnt matter..they screw right to the vent pipe and DO NOT put heat tape up there...