Air Pollution

Air pollution in Delhi drops 25% in four years


From UPSC perspective, the following things are important :

Prelims level : PM 2.5, PM 10

Mains level : Curbing air pollution in Delhi

  • Pollution levels in Delhi, primarily the concentration of particulate matter has reduced by 25% over a period of four years.
  • Five years ago, in 2014, a global study on air quality trends by the WHO had declared Delhi the most polluted city in the world.
  • Since then, the Centre, states and courts have taken several steps to arrest pollution in the city.

Delhi air pollution

  • Delhi, through its pollution control committee, started monitoring air quality in real time only in 2010.
  • It was in 2012 that Delhi saw its worst air quality due to full force of crop-residue burning that year, especially in October and November.
  • It was the first time that this burning was seriously flagged.
  • But since 2012, the average annual concentration of particulate matter — the primary cause of pollution in the city — has been falling.
  • In Delhi’s air, the primary pollutants are PM2.5 (inhalable particles of diameter 2.5 micrometres and smaller) and PM10 (10 micrometers and smaller).
  • Particulate matter, according to the US Environmental Protection Agency (EPA), is a mixture of solid particles and liquid droplets in air.
  • Some particles can be seen with the naked eye; others can only be detected under a microscope.

What data show?


  • DPCC data from 2012 to 2019 show 2018 saw the lowest average concentration of PM2.5.
  • In 2012, the annual average was 160 micrograms per cubic metre; it came down 20% to 128 micrograms/cubic m in 2018.
  • The most polluted months of the year are November, December and January, with pollution peaking in November, monthly averages between 2012 and 2018 show.
  • It is in November that the highest volume of crop residue is burnt in Haryana, Punjab and UP.
  • It is also when temperatures fall and humidity rises, aiding the increase in concentration of pollutants in the air. Locally, the burning of leaves picks up in November.
  • However, as the chart shows, PM2.5 concentrations have fallen over the years — in November as well as in the ‘cleaner’ months of July, August and September.


  • Between 2012 and 2018, the concentration of PM10 reduced by 21% from an average 351 micrograms/cubic m to 277 micrograms/cubic m.
  • PM10 is more prominent in the air in winter, primarily because of open burning and road and construction dust.
  • Until August this year, Delhi’s performance in terms of PM10 concentration has been encouraging.
  • In August, the average concentration fell to double digits for the first time since 2012; in 2013, this figure was as high as 288 micrograms/cubic m.

Seasonal variation, weather

  • Over the past five years, several studies have pointed to the fact that weather and seasons are among the biggest determinants of Delhi’s air quality.
  • No matter how much authorities try, air quality in winter will be worse than in summer.
  • Localised weather conditions also have a major role in determining air quality.
  • On a sunny and windy winter day, air quality can improve several notches within hours.
  • Weather conditions are also the reason why winters are more polluted than summers. Cold, foggy, windless days help in the accumulation of pollutants.

What has worked in Delhi

  • Between 2014 and 2017, the Delhi government has implemented orders passed by NGT to curb air pollution, including the implementation of the odd-even road rationing scheme.
  • The biggest push came in 2017, when the Centre notified the Graded Response Action Plan (GRAP), which provided state governments in Delhi and the NCR with a roadmap for action.
  • If the air was severely polluted for more than 48 hours, for example, the entry of trucks would be stopped, and all construction work halted. The GRAP also set roles for each agency, fixing accountability.
  • Shutting of the two thermal power plants in Delhi, completion of the eastern and western peripheral expressways for vehicles not destined for Delhi, a ban on PET Coke as industrial fuel, and the introduction of BS VI fuel have, experts believe, made a big difference.
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