The density of o3 is low while that of o2 is more.but why o3 is situated at top of atmosphere?

Question

The density of o3 is low while that of o2 is more.but why o3 is situated at top of atmosphere?

Answer 1

Actually, you have that backwards.  Ozone (O3) is more dense than Oxygen (O2).  Ozone is 2.14 kg/cubic meter and Oxygen is 1.43 kg/cubic meter.  However, your question is valid.  One would expect the more dense gas to be at the lower level.  Here is the explanation I found:

The main point here is that O3 is formed in the upper atmosphere and tends to stay in the O3 form before it breaks-down at lower altitiudes because of its high reactivity.

In the stratosphere, free oxygen atoms are formed when ultraviolet radiation strikes oxygen gas and breaks it up into free oxygen atoms, which can either recombine to form oxygen gas or react with other oxygen gas to form ozone. In this case, ozone is formed in the upper atmosphere and stays there.

On the other hand, free oxygen atoms can also be formed when nitrogen dioxide (NO2) is irradiated with light to form NO and O. The free oxygen can then react with O2 to form O3. Thus, ozone does form near the ground as well.



When ozone is formed near the ground, it is considered a pollutant to the air we breath. It is much more reactive than oxygen and can pose a health hazard.



In contrast, when ozone is formed in the upper atmosphere, the high reactivity of ozone allows it to filter harmful UV radiation.

Answer 2

O3  is created in the upper atmosphere by the interaction of radiation and O2