Ammonia in the air exhausted from animal containment facilities may be removed by scrubbing the air with a solution of a suitable salt of an acidic proton donor such as alum. Ammonia may be removed from the air within any enclosed animal building which includes at least one air inlet and at least one outlet, a ventilation system having an air mover effective to draw fresh air into the building through the inlet and exhaust contaminated air through the outlet, and an air scrubber in communication with the outlet. Prior to exhausting the air into the environment, the air is passed through the scrubber where it is contacted with a solution of the salt of an acidic proton donor effective for flocculating ammonia therein. The flocculated ammonia may then be removed from the solution, which may then be recycled to the scrubber.