How high in altitude could a fog reasonably exist?

Background:

I am designing an RPG world where the main characteristic is that a large fog has covered the entire fantasy planet. At the time the fog was released it was a mutating killer fog that drove the what part of the civilization to the mountains, where they have lived for thousands of years and reverted back to a renaissance level fantasy world. The some of the fog mutations because fantasy races like Elves and Dwarves, and monsters too.

At the start the fog was accident of a more advanced civilization then we are currently. In essence it was nanorobots that broken free, consuming and mutating everything in their path, that once the reproduced enough they began showing up as the fog. Over time the processing power died out and they became dormant, yet even tho they became dormant, there still was so many they were visible.

These dormant nano-biomechanical-organisms will later become the magic system. Granted because they came from advanced creation of the regular physics the magic system will not just bend the laws of physics either, so preferably

Question:

Given the fog in the background, how high in altitude could it reasonably reach to cover the entire planet, such that weather in all its extremes would not overly change the amount of fog?

I would like to drive the populations up at least 2000 feet, so they are occupying just the side of mountains, but if 1000 feet or even 500 feet is more reasonable it would be good to know.

My goal is to make it so the populations do not know what the ocean is, require zeppelins to travel between mountain ranges, last a few thousands years so the population has to revert to renaissance technology and basically avoid everything below the fog layer.

Thanks in advance

posted about 6 years ago

Richard Miller‭

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