Quote:
Originally Posted by John D Harris
Ok isn't it ozone that filters out the UV?
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If by filter out, you mean does it totally reflect and/or absorb UV, the answer is no. Some UV radiation will be be transmitted (pass thru). It depends on which band of UV light you are talking about. Remember that UV light isn't one frequency - it's an entire spectrum or band of frequencies.
Here's a couple of pics that will help explain.
The first one shows the relative intensity of the various bands of UV light at top and bottom of the atmosphere. Notice how UV-A is only minimally absorbed/reflected by ozone and only for wavelengths less then 350 nm, while virtually no UV-C is transmitted at wavelengths less than 290 nm.
The second one shows schematically where the attenuation of the various bands of UV radiation occur and the relative concentrations of ozone at various elevations.
UV-C gets absorbed in the stratosphere, UV-B starts being absorbed/reflected in between the stratopause and the tropopause while UV-A is transmitted through the tropopause all the way to the surface.
In addition, the peak ozone concentration occurs just above the tropopause.
(note: The elevations in the second graph are approximate because the tropopause is higher in the tropics, where the concentration of ozone is lower and lower at the poles where the concentration of ozone is higher.)
