The polluted air in this area has a strange smell,__ many people away.

因为实际上是:the polluted air drives many people away. 因为主语“The polluted air”与drive是主动关系，所以用现在分词。

另：He came into the classroom,followed by two students. 这里用过去分词是因为“He was followed by two students”主语He 与动词follow 是被动关系。