smog pump

I started up my 91 gt and the belt started squeaking and smoking, it's coming from around the alternator or the smog pump. I think one of them is seized. Anybody know how to tell if they're seized. And if there's any way to fix that. If it is the smog pump, can I just get a smaller belt or...

Ok, so this is kind of a long story so let me first start off with the model. It's an 89 Mustang GT (5.0). About a week ago I heard a knocking sound coming from the engine bay, so I took a look and thought the sound was coming from the alternator pulley. I took the alternator to O'reiley's and...