Percentage of tropospheric ozone in relation to total atmospheric ozone is about

Correct option is B

Introduction
· Ozone (O_3) is a triatomic molecule of oxygen that exists in two different layers of the Earth's atmosphere, serving dual roles as both a protective shield and a harmful pollutant.
· The vertical distribution of ozone is highly uneven, with the vast majority concentrated in the upper atmosphere due to the intense interaction between solar UV radiation and molecular oxygen.
· In environmental science, atmospheric ozone is often measured in Dobson Units (DU), which represent the total thickness of the ozone layer if it were compressed to standard sea-level pressure and temperature.

Information Booster
· The correct answer is 10%, which represents the fraction of total atmospheric ozone found in the troposphere (the lowest layer of the atmosphere extending from the surface to about 10–15 km).
· This tropospheric ozone is often termed "bad ozone" because it acts as a potent greenhouse gas and a secondary air pollutant that causes respiratory issues and damages vegetation.
· Unlike stratospheric ozone, it is not emitted directly but is formed through photochemical reactions involving nitrogen oxides ($NO_x$) and volatile organic compounds (VOCs) in the presence of sunlight.
· Because the density of the air is higher in the troposphere, even this small 10% fraction can lead to significant localized health impacts during "smog" events in urban areas.
· The remaining roughly 90% of the ozone resides in the stratosphere, forming the "ozone layer" that protects life on Earth by absorbing harmful ultraviolet-B radiation.

Additional Knowledge
· 90% (mentioned in statement a) refers to the concentration of ozone found in the Stratosphere, which acts as a vital UV filter; confusing these two percentages is a common error in atmospheric chemistry studies.
· 50% (mentioned in statement c) and 80% (mentioned in statement d) are incorrect values as they do not align with the scientifically established vertical profile of the atmosphere where ozone is heavily skewed toward the upper layers.
· The "Ozone Hole" phenomenon primarily occurs in the stratospheric layer (the 90% portion) over Antarctica, rather than affecting the 10% found in the tropospheric layer.
· While stratospheric ozone is essential for survival, ground-level ozone (the 10% portion) is a major component of photochemical smog and is regulated strictly under national air quality standards.