Question

Given below are two statements:
Statement (I): In the atmosphere, 90% of the ozone is distributed in the troposphere, while only 10% is confined to the stratosphere.
Statement (II): According to IPCC (2007) estimated value of radiative forcing from the tropospheric ozone is to be 0.35 \(\pm\) 0.15 W m\(^{-2}\).
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Recall which layer, troposphere or stratosphere, actually holds most of the atmosphere's ozone.

Answer 1

The Correct Option is D

This question tests two separate facts: where ozone is concentrated in the atmosphere, and the radiative forcing value the IPCC assigned to tropospheric ozone in its 2007 report.

1. Statement (I): This claims 90% of ozone sits in the troposphere and 10% in the stratosphere. That is backwards. Nearly 90% of the atmosphere's ozone is found in the stratosphere, where the ozone layer forms and blocks harmful ultraviolet rays. The troposphere holds only a small share, around 10%. So this statement is false.
2. Statement (II): This gives the IPCC (2007) radiative forcing figure for tropospheric ozone as 0.35 $\pm$ 0.15 W/m^2. The IPCC Fourth Assessment Report listed the radiative forcing of tropospheric ozone at about +0.35 W/m^2, with the uncertainty band close to this range. So this statement is true.

Since Statement (I) fails the basic fact check on ozone distribution while Statement (II) matches the IPCC (2007) figure, the correct choice is that Statement (I) is incorrect but Statement (II) is correct.

Let's summarize:

• About 90% of atmospheric ozone lies in the stratosphere, not the troposphere.
• The IPCC (2007) radiative forcing value for tropospheric ozone is close to 0.35 $\pm$ 0.15 W/m^2.

So option (4) is correct: Statement (I) is incorrect but Statement (II) is correct.