How can a trace gas (ozone <20 ppm) be vital to blocking UV in the atmosphere?

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When I think about blocking radiation, I imagine using dense solid materials, in meaningful quantities. Not a gas, let alone tiny constituents of that gas (20 ppm is 0.002%), primarily concentrated in a region of the atmosphere that is itself incredible thin. With nitrogen being 78% of the atmosphere, that means there’s at least 39,000x as much nitrogen up there, right? Eli5, how can ozone be the protective shield we think it is, and how do we know?

In: Planetary Science

3 Answers

Anonymous 0 Comments

A 9 inch line of medium point (around 1mm) sharpie weighs about 0.00000033 pounds. It blocks incoming light from reaching the surface it’s drawn on.

The air above that line weighs about 5.2 pounds.

So the sharpie, despite being about 63 ppb of the material sunlight must pass through to reach the ground, brings it to a halt. Parts per *billion*.

Put the right thing in the way and it doesn’t take very much. It doesn’t take a dense, solid material to stop light. Just a bit of sharpie.

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