Fog and haze
Thinking about all the times I've seen fog on the summit of Mount Washington, I started wondering why air that is very hazy at the bottom does not always become fog at the top. Haze implies a high moisture content, so I would think that it would cool to its dew point as it rose, resulting in a cloud, if you could see it, or fog, if you were in it. My knowledge of meteorology is rudimentary, however, so I won't speculate. I would guess it has something to do with acrobatic lapse rates and erogenous cooling.