his wife often shouts at him loudly in public 请问下为什么用介词at

shout at "对…大声喊" 是个固定的短语动词,有别于shout to 的是：shout at 带有“恼怒”“生气”等感情色彩
再如：
Don't shout at me.
不要对我叫喊.
He continually cracked his whip and shouted at the mule.
他不住地挥着鞭子,吆喝骡子.
There is no need to shout angry words at me.
用不着冲我嚷.