Context: According to an analysis by the Centre for Science and Environment (CSE) , particulate matter and nitrous oxide levels fell during the lockdown, but ozone increased in several cities.

More on news:

  • The analysis was based on Central Pollution Control Board (CPCB) data from 22 cities in 15 States in lockdown days considered from March 25 to May 31. 
  • It emerged that more than two-thirds of the lockdown days in Delhi-NCR cities and Ahmedabad had at least one observation station that exceeded the standard. 
  • In Ahmedabad, the city-wide maximum eight-hour average of ozone exceeded the standard on 43 days; in Ujjain, it exceeded 38 days. 
  • The standard used was that of the United States Environmental Protection Agency norms.
  • The city-wide maximum average of ozone in Gurugram exceeded the standard on 26 days — at least one observation station exceeded the standard on 57 days.
  • Particulate pollution dropped dramatically during the lockdown. 
    • Average PM 2.5 levels during the lockdown for all cities were found to be lower than the average for the same period in 2019. 

Ozone pollution:

  • Ozone is primarily a “sunny weather problem” in India, that otherwise remains highly variable during the year. 
  • It is a highly reactive gas,even short-term exposure of an hour is dangerous for those with respiratory conditions and asthma and that’s why an eight-hour average is considered for ozone instead of the 24-hour average for other pollutants.
  • Ozone is not directly emitted by any source but is formed by photochemical reactions between oxides of nitrogen (NOx) and other volatile organic compounds (VOCs) and gases in the air under the influence of sunlight and heat.
  •  It can be curtailed only if gases from all sources are controlled.


  • Centre for Science and Environment (CSE) is a not-for-profit public interest research and advocacy organisation based in New Delhi, India. 
  • Established in 1980, CSE works as a think tank on environment-development issues in India, poor planning, climate shifts devastating India's Sundarbans and advocates for policy changes and better implementation of the already existing policies. 
  • CSE uses knowledge-based activism to create awareness about problems and propose sustainable solutions.



  • The Central Pollution Control Board (CPCB) of India is a statutory organisation under the Ministry of Environment, Forest and Climate Change . 
  • It was established in 1974 under the Water (Prevention and Control of pollution) Act, 1974.
  • The CPCB is also entrusted with the powers and functions under the Air (Prevention and Control of Pollution) Act, 1981. 
  • It serves as a field formation and also provides technical services to the Ministry of Environment and Forests under the provisions of the Environment (Protection) Act, 1986. 



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