I have found a very interesting video surfing the net. It deals with the main factors that affect the UV radiation reaching the Earth’s surface. In five minutes, it explains clearly the role of atmospheric and astronomical factors on the variability of UV radiation levels at surface. This video could be very useful for academic purposes.
You can see the video “Increasing ultraviolet radiation levels” at:
http://www.clinuvel.com/en/news/webcasts/item/1307-increasing-ultraviolet-levels