system
Given the following post, respond as if you're commenting on Reddit:
human
Are you at greater risk of sunburn up on a mountain?

 I remember being told that sunburns are more likely when you're up in the mountains because the air is thinner. And that's why Andean peoples wear wide brim hats most of the time. And I think my own experience matches that. I've burnt pretty quickly when up in mountainous terrain.

But I also know (believe) that UV is mostly blocked by the ozone layer. And the ozone layer goes from 33,000 feet to 165,000 feet. So even on top of Everest you're fully under it. So it shouldn't matter how high you walk. You should still be protected.

So what's going on? Which part of what I think I know is wrong?
gpt
The ultraviolet spectrum is pretty broad (400 nm – 10 nm) and is divided into three sub-bands. Ozone is really good at absorbing the short UV-C wavelengths and moderately good at absorbing the medium UV-B wavelengths. UV-A and UV-B (which are responsible for sunburns and skin cancer) are mostly absorbed by water vapor and other atmospheric gases, which is why being at sealevel offers more protection than on a mountain.