The overall air quality index (AQI) Thursday was recorded in the "severe plus emergency" category at 642, according to Centre-run System of Air Quality and Weather Forecasting and Research (SAFAR) data.
In 2017, the AQI was recorded at 367, a day after Diwali, while in 2016 it was 425. The AQI this year was over twice that of 2017.
A "severe plus emergency" AQI essentially means that even healthy people may suffer from respiratory illnesses on prolonged exposure. This air will seriously affect those with ailments, according to a SAFAR advisory.
The Supreme Court had allowed people to burst firecrackers from 8 pm to 10 pm only on Diwali and other festivals. The top court also allowed manufacture and sale of just "green crackers" which have low emission of light, sound and harmful chemicals.
"Last year Diwali was observed on October 19 whereas this year, the festival was celebrated on November 7 which has different meteorological conditions that govern the dispersion pattern of pollutants," the CPCB said.
It admitted that the severe deterioration of air quality was due to unfavourable conditions coupled with pollutants generated from firecrackers.
However, the CPCB said when compared with the average particulate matter data during November 1 to 7 last year with the same period this year, the city average particulate concentration for Delhi was lower in 2018.
It said that it can be observed that all the pollutants reported higher values at all the stations if compared with 2017 data for pre-Diwali.
"This may be due to the differences in background air quality status in October and November. Meteorology as well as stubble burning makes huge difference in Delhi's air quality in late October and November.
"This year, Diwali day shows that the PM10 and PM2.5 values have increased this year compared to 2017. However, the data are similar to Diwali day of 2016 which was observed on October 30," the CPCB data said.
Giving a break up of different areas, the CPCB said in Pritampura, the PM10 and PM2.5 levels was 831 and 990 respectively this year, while last year the PM10 and PM2.5 was recorded at 677 and 690 respectively.
In Janakpuri, the PM10 and PM2.5 levels was 1076 and 998 respectively this year, while last year it was recorded at 706 and 638 respectively
In ITO, PM10 and PM2.5 was recorded at 470 and 322 respectively this year, while last year it was recorded at 438 and 180 respectively.
On noise pollution, the CPCB data showed increasing trend as compared to 2017.
"Only at Anand Vihar and Punjabi Bagh both day time and night time noise level declined. DCE, Dilshad Garden, ITO, Mandir Marg, Dwarka and R.K. Puram recorded increase in both day and night time noise observed on 1st November 2018 compared to selected pre-Diwali day in 2017," CPCB data said.
According to SAFAR, on Thursday, the PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) level was recorded more than eight times the permissable limit at 492 gm-3.The PM10 (particles in the air with a diameter of less than 10 micrometres) level was recorded six times the permissable limit at 618 gm-3.
In 2017, official data showed the PM10 level reached 595 gm-3 and PM2.5 was 407 gm-3. India's official permissible PM2.5 limit is 60 gm-3 while PM10 level is 100 gm-3.
The sharp spike in pollution is caused by rampant burning of firecrackers that has led to the formation of a smoky layer across the national capital and drastically reduced visibility, authorities said.
The SAFAR had warned that even if partial toxic firecrackers as compared to last year were burnt, then the air quality would fall in the "severe" category.
In certain places firecrackers were burnt before and after the set time frame, despite the Supreme Court's order.
The court had said police should ensure that there was no sale of banned firecrackers and in case of any violation, the station house officer (SHO) of the police station of the area would be held personally liable and this would amount to committing contempt of the court.
The areas where the violations were recorded included Mayur Vihar Extension, Lajpat Nagar, Lutyens' Delhi, IP extension, Dwarka and Noida Sector 78.