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At first I wanted to use term "Mean free path" in title but I know it means other kinds of interactions too,not just absorbtion.What I really mean is mean free path but only for absorbtion.

For example,if I have 253 nm laser,and I shine it in air,how far will the beam travel before losing 50% of its power due to absorbtion by air molecules and atoms?

EDIT : I would like to clarify that I mean air at low altitude,close to sea level,like in a city.I realized someone might whip out absorbtion spectrum as photons from space and sun experience as they travel through ozone layer to surface of earth.Such graph would be totaly useless becose gas at low altitude have different pressure and composition,most significant is much lower content or ozone.

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    $\begingroup$ A wavelength of 253 nm corresponds to a photon energy of 4.9 eV. The absorption length in air should be very long. And it would depend on impurities. $\endgroup$ – Pieter Mar 2 '18 at 12:37
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    $\begingroup$ Indeed, that is quite near quadrupled Nd:YAG, and you can send that all over the place in the labe without worrying about air absorption at all. $\endgroup$ – Jon Custer Mar 2 '18 at 14:03

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