In its report, CPCB found that Delhi-National Capital Region (NCR) is the worst impacted in the country by high Ozone (O3) pollution, followed by Mumbai Metropolitan Region (MMR).

About Ozone 

• Ozone (O3) is a variant of oxygen composed of three oxygen atoms. It occurs in two layers of the atmosphere: the stratosphere (upper layer) and the troposphere (ground level up to 10km).
  • In the stratosphere, ozone protects life on Earth from the sun’s ultraviolet radiation. 
  • In the troposphere, it is an air pollutant. 
• The safe eight-hourly ozone standard is set at 100 micrograms per cubic metre (µg/m³), while the one-hour limit is 180µg/m³. 

Ground-level Ozone (GLO) 

• GLO is a secondary, short-lived pollutant that remains in the atmosphere for only hours to weeks. 
• Factor Responsible: Created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC). 
  • Anthropogenic sources: Transportation, power plants, residential, agricultural activities. , etc. 
  • Natural sources: Soil-based emissions of NOx, and wildfire-induced CO and biospheric methane emissions.