The atmosphere, the part that gives us the weather extends up to about 12 kilometers. This is about 7 miles upwards! It is not so thick is it? Just think from Goleta to Santa Barbara it is about 15 kilometers!! Much great length than the depth of the atmosphere. This is why even small amount of pollution have such a big impact.
We think the atmosphere goes on for ever and ever but it does not, it is just a little fishbowl and when we dump toxic materials and CO2 we are affecting it easily.
Anyway above the troposphere lies the stratosphere. This is a very low pressure region and this is where ozone is concentrated, Ozone is O3. The oxygen we breathe is O2, but way above most of the air in the stratosphere, photons from the sun cause reactions that make O3 from O2.
So, the ozone layer is this region of the stratosphere where ozone is concentrated.