On Wed, 29 May 2019 14:20:15 -0700, Nicholas Randall wrote:


...With altitude, at the top of a mountain UV levels are higher
because the air is thinner and cleaner.


It's not really related to how thin the air is but because the UV photons
have travelled through less atmosphere and so are attenuated less.

If the air pressure was the same at the top and bottom of a mountain the
UV would still be higher at the top.


--
Brian Wakem
Lower Bourne, Farnham, Surrey
http://www.brianwakem.co.uk/weather
Live obs @ 15:17:31 : 20.9C, DP 15.7C, RH 72%, 0.0 mm