"I live in Xi'an."
Usually when you tell someone where you live, it's a simple statement/fact, so you don't have to express "certainty" or "exclamation" or any other tone that is related to the character 啊, so you don't have to add it.
But in certain cases, for example when some friend of yours suddenly forgets where do you live and asks "诶你住哪儿来着？" with a connotation of "remind me", you can add an “啊” to express exclamation/disbelief “我住在西安啊!”, and the connotation is "how can you forget that!"/"you'd better take note this time"/"Of course I'm from Xi'an, where else?"
Another example is when someone asks whether you live in Xi'an “你住西安吗？”, and it's more of a guess/out-of-the-blue question, you can reply with “我不住西安啊” to express a feeling of "Why would you think that I live in Xi'an?" or "Why ask all of a sudden?".