no filter on mine.. i actually popped the cover off the first time last month when the windshield washer line popped off and was dumping rain-x.
if youre smelling outside odors you dont like, set the air selector to interior recirculation.. that will resolve your problem completely. the hvac must be OFF of defrost. defrost uses outside air by default.
BTW...
the reason no airfilter was fitted to the challenger from the factory...
is because it wasnt designed to follow. it was designed to lead. get off your ass and pass people, you wont be left sucking exhaust.