UVA is far more abundant, but UVB is much higher energy than UVA. So UVB has a far greater damage potential in comparison. I think this article - with loads of references can help a lot. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3709783/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3709783/