One of my co-workers insists that all the harmful UV from sunlight is filtered out by the atmosphere by the time you get to the altitude of the Dead Sea (~1300 feet below sea level). She saw this in a documentary. It doesn’t seem likely to me. Does anyone out there know?
UV is primarily filtered out by the ozone layer, which lies at an altitude of between 9 and 64 km (estimates vary greatly). It filters out some 99% of the dangerous UV-B and UV-C rays from the sun. Any filtering by other regions of the atmosphere is negligible in comparison, so below this layer, altitude plays essentially zero role in UV level.