here it is given that ozone is one of the gases that cause greenhouse effect but it also protects us from harmful uv rays of sun.So, the ozone gas is harmful for us or not?
Your query is quite obvious. Let us understand this in detail.
The upper stratosphere consists of considerable amount of ozone (O3) which protects us from the harmful ultraviolet radiation coming from the sun. In the upper atmosphere ozone is a product of ultraviolet radiation acting on dioxygen (O2) molecules according to the following reactions.
Ozone is thermodynamically unstable. It absorbs the U.V. radiations to give dioxygen along with the liberation of heat which raises the temperature of the stratosphere.
In this manner, there exists a dynamic equilibrium between the production and decomposition of ozone.
So, now you must have understood that though ozone is a greenhouse gas, yet this layer is very significant as it protects us from the harmful effect of ultraviolet radiations.
I hope, the answer is clear to you. Even then, if you counter any problem in understanding this, do write back to us. We will be happy to help you.