Ground-level Ozone

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According to CSE analysis, parts of Delhi NCR is experiencing ground-level ozone levels above the national standards on 87/ 92 days in summer (March-May).


  • Also known as tropospheric ozone
  • It is a colourless irritating gas that forms near the surface i.e. up to 2 miles above ground.
  • It is a secondary pollutant formed by interaction between primary pollutants.


  • Can travel long distances and pollute regions far away from source i.e. even rural areas could be affected.
  • Has serious health consequences:
    • Inflammation and damage of airways
    • Increased susceptibility of lungs to infections
    • Aggravates conditions like:
      • Asthma
      • Emphysema
      • Chronic bronchitis
  • Negatively impacts:
    • Sensitive vegetation
    • Sensitive ecosystems


  • Formed by reaction between:
    • NOx- nitrogen oxides
    • VOCs- volatile organic compounds
  • These two primary pollutants are emitted by natural and anthropogenic sources.
  • 95% of NOx comes from anthropogenic activities like burning of coal and oil.
  • VOCs are emitted by:
    • Gasoline combustion and marketing
    • Upstream oil and gas production
    • Combustion of wood
    • Evaporation of liquid fuels and solvents


  • Ground-level ozone usually breaches safety levels on hot summer days, especially in urban areas.
  • It could also reach high levels in colder months.

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