According to the System of Air Quality and Weather Forecasting (Safar) and the Central Pollution Control Board (CPCB), the overall air quality index (AQI) of Delhi, which was at 47, falling in the good category.
The level of PM2.5 was recorded at 17 and the PM10 level was recorded at 31 on Friday, Safar said.
In comparison, the AQI in New York was recorded at "good" at 17, at 34 in Frankfurt, while in London, it was "moderate" at 52.
A CPCB scientist said that in 2017, the city had witnessed the AQI recorded below 50 - at 42, but could not recall the exact date.
The CPCB is recording AQI since 2015 and such good conditions have not been seen in the last four years.
Gufran Baig, scientist and programme director, SAFAR, said that this is the lowest AQI recorded this year and it will remain good for another two to three days.
He said that the air quality has improved due to widespread rain received in the northern parts of the country.
"Rajasthan, Himachal Pradesh, Punjab, Haryana and Uttar Pradesh, all areas surrounding are receiving a good amount of rainfall this year which is improving the air condition in the city. Such kind of rain was never received earlier so the air quality has never reached this level," Baig said.
Mahesh Palawat, Vice President, Meteorology and Climate Change, at private forecaster Skymet Weather told that this was the longest spell of clean air experienced by Delhiites.
"The widespread rain has helped in improving air quality in Delhi as well as in Noida and Gurugram. Increased rainfall activity is likely to bring more respite in coming days," he said, adding that the rain has helped in settling down pollutants.
( With inputs from IANS )