On Tuesday, 26 May 2020 20:09:50 UTC+1, Graham Easterling wrote:
I agree with most of what you state about factors that affect UV levels except humidity. I do not think it affects them.

Nicholas
Meir Heath, Stoke-On-Trent 250 metres above sea level.

Equally, I am sure it does. If Norman reads this I know he'll agree. In fact, anyone that spends a lot of time outdoors, certainly on the coast of SW England where high humidity is common, fully appreciates the fact.

How else do you explain the big drop in UV when a cold front goes through? Certainly lower high level ozone sometimes being associated with a warm sector ridge is partly the cause, but the whole thing? If you don't except it's the humidity, despite the evidence, you need to come up with an alternative explanation why it's so high in air which has none of the clarity of that behind the cold front.

Somewhere I'v got a list of times when the Camborne UV has hit 9, never in clear, clean sunny mP conditions.

Graham
Penzance

I have not seen any evidence UV levels are linked to high humidity. If UV levels are lower after a cold front it may be there is more cloud.

Nicholas
Meir Heath, Stoke-On-Trent 250 metres above sea level.