Haze

UV filter can reduce the haziness created by UV rays. Personaly I haven't seen it as a major problem (well, I do use an UV filter). If the interest's in the foreground, haziness in the distance can perhaps be used as an advantage?

I know what you mean, really makes the photo look bad. On the other hand you are recording a fact and should you alter it. I had a conversation with a chap the other day and he told me he never alters what the camara sees especialy if it records the truth. Polution is a fact of life, I would leave it in.