Besides the way it's written? :P 啊 is phonetic, (in direct address and exclamation) 阿(childhood name) , (a monosyllabic personal name or surname)

“啊”是感叹词。例：1.啊，好难！2.天啊！你在干什么？ “阿”当读“a”的时候，一般使用于名字的昵称中。例：阿凡达、阿雅 “啊”is an interjection. for example：1.啊，too difficult. 2.天啊！what are you doing? When pronunciation of “阿”is "a", it's often in the nickname. for example:阿凡达、阿雅