I think the increased UVA poses the most risk of damage. I don't know of any metabolic use for UVA. As the article notes, tanning beds have a far worse UVB:UVA ratio than sunlight.

Because UVB scatters more than UVA (Rayleigh scattering), shade increases the UVB:UVA ratio from 1:1 to about 0.52:0.35 under a shade umbrella, or 0.53:0.37 under a tree. See Table 1 (paywalled, sorry) https://doi.org/10.1016/j.jsbmb.2005.04.039

of course, most that go to a tanning booth care more about looks than health