Air Pollution

What is Urban Ozone?


From UPSC perspective, the following things are important :

Prelims level: Urban Ozone

Mains level: Good and Bad Ozone

A Manchester (UK) based research has found that the nationwide lockdown may be leading to the generation of a dangerous pollutant, urban ozone.

The Ozone is formed due to different factors in the Troposphere and the Stratosphere (where the ozone acts as a protective layer). Note these differences from prelims perspective.

Urban Ozone

  • The photochemical production of ozone may become more important in urban areas during summertime in these low conditions of oxides of nitrogen.
  • As nitrogen oxides reduce, photochemical production may become more efficient and can lead to higher ozone concentrations in the summertime.
  • The higher summer temperatures increase emissions of biogenic hydrocarbon from natural sources such as trees. These biogenic hydrocarbons significantly affect urban ozone levels.
  • While ozone is important for screening harmful solar UV radiation when present higher up in the atmosphere, it can be a danger at the Earth’s surface and can react to destroy or alter many biological molecules.

Back2Basics: Ozone Gas

  • It is a gas that occurs both in the Earth’s upper atmosphere and at ground level.
  • Ozone occurs in two layers of the atmosphere. The layer closest to the Earth’s surface is the troposphere.
  • Here, ground-level or “bad” ozone is an air pollutant that is harmful to breathe and it damages crops, trees and other vegetation. It is the main ingredient of urban smog.
  • The stratospheric or “good” ozone protects life on Earth from the sun’s harmful ultraviolet (UV) rays.

Formation of Ozone

  • Ozone is produced naturally in the stratosphere when highly energetic solar radiation strikes molecules of oxygen, and cause the two oxygen atoms to split apart in a process called photolysis. If a freed atom collides with another O2, it joins up, forming ozone.
  • The majority of tropospheric ozone formation occurs when nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs), react in the atmosphere in the presence of sunlight, specifically the UV spectrum.

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