First of all, welcome to the forum. Secondly, a kind word of advice; it is better to post renders (or any images) as jpg's. Small (as not to overload the server, like with png's), and easily viewed. A pdf has to be opened separately, which will discourage people.
Haze has to do with the size of the scene. It's all world space, so the larger the terrain you see, the more hazy in the distance. If you search for 'haze settings' or 'atmosphere settings' you'll probably find heaps of threads covering all questions ever asked about this. And it's good to experiment with settings too. Just change one variable at the time (maybe even with an extreme setting, don't forget that you can use the slider, but also fill in numbers manually, even negative), render a small crop and see what happens. Or check it out in the RT/PT preview window.