First off, newbie here.
I've tried with some difficulty to answer my own question, but it would be helpful to get some experienced answers. I was recently in Europe and I've noticed that many of my pictures have a haze in the background. Sometimes it appears slightly bluish, which I understand may be due to UV light...but I'm not sure if that's really the problem. I was never at very high altitude, and the problem seems to be greatest in pictures I shot around noontime, which leads me to think a polarizing filter might help.
If it's relevant, I have a Nikon D70, Nikkor 28-100 mm 1:3.5-5.6 G lens.
Any help or suggestions would be greatly appreciated!

It could just be haze. Try looking up "local contrast" on this site. That might help.

Also, were you using a lens hood?

Polarizers are less effective at mid-day. Noon would not be an ideal time to use one and get much result. I never experienced much satisfaction with UV filters in my film days, but don't base anything on my empirical experience with UVs.

I have found that distant deep blue softness is generally haze. If it is distractive, I can use Photoshop to either reduce or accent it for a more pleasing rendition.

The local contrast suggestion will "cut the haze" as well, but the blue tint remains to be dealt with.

One of the photo.net guys (Bob Atkins?) did a test of UV filters. I think the only one that did much was the tiffen.