怒气冲冲 is an AABB reduplication idiom (怒气 + 冲冲). It functions as an adjectival predicate or pre-verbal adverbial. The 冲冲 reduplication intensifies the sense of anger surging upward.
memory
Picture anger (怒气) surging upward (冲冲 = rushing up) like steam — someone so mad they are literally blowing off steam.