Well, there is definitely more to just density.
Glass is transparent to visible light, but it is opaque to UV and infrared. Bathroom tissue is opaque to visible light.
It might as well that Ozone layer has little density. But as long as ozone layer as a whole is, to some degree, opaque to UV, UV will be absorbed in the corresponding wavelengths.
It does not matter how many school degrees one has. If one knows what’s happening, s/he should speak the truth. If one does not, s/he should learn.