The 阿 particle (character) is used to add emphasis to a sentence. You could think of 阿 as being similar to an exclamation mark. Here are some examples:
对阿！
duì ā!
Correct!
是阿！
shì ā!
Yes / Yeah!
好啊。
hǎo a.
Great / Fine
太贵阿！
tài guì ā!
Too Expensive!
很棒阿。
hěn bàng ā.
Really great.
It’s not necessary to use an exclamation mark when using 阿, however doing so conveys extra emphasis. Equally, you could write the above examples without the 阿 character, however, this would remove some of the emphasis. Leaving off 阿 is somewhat like saying “really great” or “correct” in English without any tonality or emphasis in your speech, leaving your statement lacking emotion.
