What effects would a massive amount of water vapor in the atmosphere have on an alien planet

I am an aspiring science-fiction novelist. I am experimenting with a world I'm trying to create and I wanted a couple of expert opinions on Atmospheric composition;

53% Nitrogen 27% Oxygen 3% Xenon 15% Water Vapor 2% Carbon Dioxide

Off the bat, the air isn't supposed to be breathable for traditional earth-based life. It is inhabited by a couple of cultures (most primitive being Neolithic hunter-gatherers, most advanced Iron Age equivalent to the Viking Age), it has a lighter gravity than earth with twice the atmosphere and I am curious what would happen to an explorer from Earth if their breathing mask was removed.

Edit: by twice the atmosphere I mean the atmosphere is twice as thick, allowing more massive creatures to fly.

posted over 5 years ago

Jacob Badger‭

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