I don't think that helps significantly. Check out the plot on Wikipedia [1] for the ultraviolet index in NYC. At peak on summer, solar noon versus 8am there's a

I don't think that helps significantly. Check out the plot on Wikipedia [1] for the ultraviolet index in NYC. At peak on summer, solar noon versus 8am there's a factor of ~3 difference between UV incident on a horizontal surface. Since the sun is much lower at 8am, that factor is primarily from the surface being at an oblique angle to the sun. So atmospheric absorption is significantly smaller than a factor of 3 and since much of the human body is not oriented horizontally, that's the part I'd want to be considering. Either way though, SPF of at most 3 is insufficient. [1] https://en.wikipedia.org/wiki/Ultraviolet_index https://en.wikipedia.org/wiki/Ultraviolet_index