Context: Going by a report of  the Central Pollution Control Board, Delhi’s particulate matter(PM) pollution has reduced to nearly half of the earlier levels during the first phase of the lockdown.

More on the news:

  • On an overall level, 46% reduction in PM2.5 and 50% reduction in PM10 was observed during the lockdown period.
    • This led to nearly a week-long run of the air quality index remaining in the Good and Satisfactory categories, in contrast to the earlier unhealthy and hazardous categories. 
    • Moreover, 24-hourly average PM2.5 and PM10 were within National Ambient Air Quality Standards (NAAQS) for nearly the last two weeks.
  • Nearly 78% of cities in the country that are monitored by the CPCB had their AQI in the good and satisfactory categories, in contrast to the pre-lockdown average of 44%.

Probable Causes

  • The improvement in air was due to a reduction in combustion and industrial sources which are common to both PM2.5 and PM10.
    • As 81% of Delhi’s nitrous oxide emissions came from the transport sector, restrictions on vehicular activity during lockdown led to a 56% reduction in NO2 levels and over 37% reduction in CO levels.
    • There was also a 47% reduction in benzene levels too.
    • SO2 levels were reduced only by 20% owing to continued operation of power plants,restaurants and some industries, along with biomass/refuse burning in some areas in and around Delhi.

Lastly, it needs to be seen how long this gain continues to be. These figures will be tested against the coming Dust storm, and summers, and most importantly increased economic activity post lockdown phase.


National Ambient Air Quality Standards (NAAQS)

As per the provisions of Air (Prevention and Control of Pollution) Act,1981 the Central Pollution Control Board is empowered to set standards for the quality of air.

  1. Current NAAQS were notified by CPCB in 2009.
  2. Pollutants covered under NAAQS are Sulphur Dioxide (SO2), Nitrogen Dioxide (NO2), Particulate Matter (PM 10, PM 2.5), Ozone (O3), Lead (Pb), Carbon Monoxide (CO), Ammonia (NH3), Benzene (C6H6), Benzo(a)Pyrene (BaP), Arsenic(As), Nickel (Ni).



  • It is a statutory organisation, constituted in September, 1974 under the Water (Prevention and Control of Pollution) Act, 1974. 
  • Further, CPCB was 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 of the provisions of the Environment (Protection) Act, 1986. 
  • Principal Functions of the CPCB, as spelt out in the Water (Prevention and Control of Pollution) Act, 1974, and the Air (Prevention and Control of Pollution) Act, 1981, 
    • To promote cleanliness of streams and wells in different areas of the States by prevention, control and abatement of water pollution, and 
    • To improve the quality of air and to prevent, control or abate air pollution in the country.


Air Quality Index


  • Air Quality Index is a tool for effective communication of air quality status to people in terms, which are easy to understand. 
  • It transforms complex air quality data of various pollutants into a single number (index value), nomenclature and colour.
  • It is describe as ‘One Number- One Colour-One Description’ for the common man to judge the air quality within his vicinity